linux/kernel/futex.c
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   1/*
   2 *  Fast Userspace Mutexes (which I call "Futexes!").
   3 *  (C) Rusty Russell, IBM 2002
   4 *
   5 *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
   6 *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
   7 *
   8 *  Removed page pinning, fix privately mapped COW pages and other cleanups
   9 *  (C) Copyright 2003, 2004 Jamie Lokier
  10 *
  11 *  Robust futex support started by Ingo Molnar
  12 *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
  13 *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
  14 *
  15 *  PI-futex support started by Ingo Molnar and Thomas Gleixner
  16 *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  17 *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
  18 *
  19 *  PRIVATE futexes by Eric Dumazet
  20 *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
  21 *
  22 *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
  23 *  Copyright (C) IBM Corporation, 2009
  24 *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
  25 *
  26 *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
  27 *  enough at me, Linus for the original (flawed) idea, Matthew
  28 *  Kirkwood for proof-of-concept implementation.
  29 *
  30 *  "The futexes are also cursed."
  31 *  "But they come in a choice of three flavours!"
  32 *
  33 *  This program is free software; you can redistribute it and/or modify
  34 *  it under the terms of the GNU General Public License as published by
  35 *  the Free Software Foundation; either version 2 of the License, or
  36 *  (at your option) any later version.
  37 *
  38 *  This program is distributed in the hope that it will be useful,
  39 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  40 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  41 *  GNU General Public License for more details.
  42 *
  43 *  You should have received a copy of the GNU General Public License
  44 *  along with this program; if not, write to the Free Software
  45 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  46 */
  47#include <linux/slab.h>
  48#include <linux/poll.h>
  49#include <linux/fs.h>
  50#include <linux/file.h>
  51#include <linux/jhash.h>
  52#include <linux/init.h>
  53#include <linux/futex.h>
  54#include <linux/mount.h>
  55#include <linux/pagemap.h>
  56#include <linux/syscalls.h>
  57#include <linux/signal.h>
  58#include <linux/export.h>
  59#include <linux/magic.h>
  60#include <linux/pid.h>
  61#include <linux/nsproxy.h>
  62#include <linux/ptrace.h>
  63#include <linux/sched/rt.h>
  64#include <linux/hugetlb.h>
  65#include <linux/freezer.h>
  66
  67#include <asm/futex.h>
  68
  69#include "rtmutex_common.h"
  70
  71int __read_mostly futex_cmpxchg_enabled;
  72
  73#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
  74
  75/*
  76 * Futex flags used to encode options to functions and preserve them across
  77 * restarts.
  78 */
  79#define FLAGS_SHARED            0x01
  80#define FLAGS_CLOCKRT           0x02
  81#define FLAGS_HAS_TIMEOUT       0x04
  82
  83/*
  84 * Priority Inheritance state:
  85 */
  86struct futex_pi_state {
  87        /*
  88         * list of 'owned' pi_state instances - these have to be
  89         * cleaned up in do_exit() if the task exits prematurely:
  90         */
  91        struct list_head list;
  92
  93        /*
  94         * The PI object:
  95         */
  96        struct rt_mutex pi_mutex;
  97
  98        struct task_struct *owner;
  99        atomic_t refcount;
 100
 101        union futex_key key;
 102};
 103
 104/**
 105 * struct futex_q - The hashed futex queue entry, one per waiting task
 106 * @list:               priority-sorted list of tasks waiting on this futex
 107 * @task:               the task waiting on the futex
 108 * @lock_ptr:           the hash bucket lock
 109 * @key:                the key the futex is hashed on
 110 * @pi_state:           optional priority inheritance state
 111 * @rt_waiter:          rt_waiter storage for use with requeue_pi
 112 * @requeue_pi_key:     the requeue_pi target futex key
 113 * @bitset:             bitset for the optional bitmasked wakeup
 114 *
 115 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
 116 * we can wake only the relevant ones (hashed queues may be shared).
 117 *
 118 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
 119 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
 120 * The order of wakeup is always to make the first condition true, then
 121 * the second.
 122 *
 123 * PI futexes are typically woken before they are removed from the hash list via
 124 * the rt_mutex code. See unqueue_me_pi().
 125 */
 126struct futex_q {
 127        struct plist_node list;
 128
 129        struct task_struct *task;
 130        spinlock_t *lock_ptr;
 131        union futex_key key;
 132        struct futex_pi_state *pi_state;
 133        struct rt_mutex_waiter *rt_waiter;
 134        union futex_key *requeue_pi_key;
 135        u32 bitset;
 136};
 137
 138static const struct futex_q futex_q_init = {
 139        /* list gets initialized in queue_me()*/
 140        .key = FUTEX_KEY_INIT,
 141        .bitset = FUTEX_BITSET_MATCH_ANY
 142};
 143
 144/*
 145 * Hash buckets are shared by all the futex_keys that hash to the same
 146 * location.  Each key may have multiple futex_q structures, one for each task
 147 * waiting on a futex.
 148 */
 149struct futex_hash_bucket {
 150        spinlock_t lock;
 151        struct plist_head chain;
 152};
 153
 154static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
 155
 156/*
 157 * We hash on the keys returned from get_futex_key (see below).
 158 */
 159static struct futex_hash_bucket *hash_futex(union futex_key *key)
 160{
 161        u32 hash = jhash2((u32*)&key->both.word,
 162                          (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
 163                          key->both.offset);
 164        return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
 165}
 166
 167/*
 168 * Return 1 if two futex_keys are equal, 0 otherwise.
 169 */
 170static inline int match_futex(union futex_key *key1, union futex_key *key2)
 171{
 172        return (key1 && key2
 173                && key1->both.word == key2->both.word
 174                && key1->both.ptr == key2->both.ptr
 175                && key1->both.offset == key2->both.offset);
 176}
 177
 178/*
 179 * Take a reference to the resource addressed by a key.
 180 * Can be called while holding spinlocks.
 181 *
 182 */
 183static void get_futex_key_refs(union futex_key *key)
 184{
 185        if (!key->both.ptr)
 186                return;
 187
 188        switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
 189        case FUT_OFF_INODE:
 190                ihold(key->shared.inode);
 191                break;
 192        case FUT_OFF_MMSHARED:
 193                atomic_inc(&key->private.mm->mm_count);
 194                break;
 195        }
 196}
 197
 198/*
 199 * Drop a reference to the resource addressed by a key.
 200 * The hash bucket spinlock must not be held.
 201 */
 202static void drop_futex_key_refs(union futex_key *key)
 203{
 204        if (!key->both.ptr) {
 205                /* If we're here then we tried to put a key we failed to get */
 206                WARN_ON_ONCE(1);
 207                return;
 208        }
 209
 210        switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
 211        case FUT_OFF_INODE:
 212                iput(key->shared.inode);
 213                break;
 214        case FUT_OFF_MMSHARED:
 215                mmdrop(key->private.mm);
 216                break;
 217        }
 218}
 219
 220/**
 221 * get_futex_key() - Get parameters which are the keys for a futex
 222 * @uaddr:      virtual address of the futex
 223 * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
 224 * @key:        address where result is stored.
 225 * @rw:         mapping needs to be read/write (values: VERIFY_READ,
 226 *              VERIFY_WRITE)
 227 *
 228 * Return: a negative error code or 0
 229 *
 230 * The key words are stored in *key on success.
 231 *
 232 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
 233 * offset_within_page).  For private mappings, it's (uaddr, current->mm).
 234 * We can usually work out the index without swapping in the page.
 235 *
 236 * lock_page() might sleep, the caller should not hold a spinlock.
 237 */
 238static int
 239get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
 240{
 241        unsigned long address = (unsigned long)uaddr;
 242        struct mm_struct *mm = current->mm;
 243        struct page *page, *page_head;
 244        int err, ro = 0;
 245
 246        /*
 247         * The futex address must be "naturally" aligned.
 248         */
 249        key->both.offset = address % PAGE_SIZE;
 250        if (unlikely((address % sizeof(u32)) != 0))
 251                return -EINVAL;
 252        address -= key->both.offset;
 253
 254        /*
 255         * PROCESS_PRIVATE futexes are fast.
 256         * As the mm cannot disappear under us and the 'key' only needs
 257         * virtual address, we dont even have to find the underlying vma.
 258         * Note : We do have to check 'uaddr' is a valid user address,
 259         *        but access_ok() should be faster than find_vma()
 260         */
 261        if (!fshared) {
 262                if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
 263                        return -EFAULT;
 264                key->private.mm = mm;
 265                key->private.address = address;
 266                get_futex_key_refs(key);
 267                return 0;
 268        }
 269
 270again:
 271        err = get_user_pages_fast(address, 1, 1, &page);
 272        /*
 273         * If write access is not required (eg. FUTEX_WAIT), try
 274         * and get read-only access.
 275         */
 276        if (err == -EFAULT && rw == VERIFY_READ) {
 277                err = get_user_pages_fast(address, 1, 0, &page);
 278                ro = 1;
 279        }
 280        if (err < 0)
 281                return err;
 282        else
 283                err = 0;
 284
 285#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 286        page_head = page;
 287        if (unlikely(PageTail(page))) {
 288                put_page(page);
 289                /* serialize against __split_huge_page_splitting() */
 290                local_irq_disable();
 291                if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) {
 292                        page_head = compound_head(page);
 293                        /*
 294                         * page_head is valid pointer but we must pin
 295                         * it before taking the PG_lock and/or
 296                         * PG_compound_lock. The moment we re-enable
 297                         * irqs __split_huge_page_splitting() can
 298                         * return and the head page can be freed from
 299                         * under us. We can't take the PG_lock and/or
 300                         * PG_compound_lock on a page that could be
 301                         * freed from under us.
 302                         */
 303                        if (page != page_head) {
 304                                get_page(page_head);
 305                                put_page(page);
 306                        }
 307                        local_irq_enable();
 308                } else {
 309                        local_irq_enable();
 310                        goto again;
 311                }
 312        }
 313#else
 314        page_head = compound_head(page);
 315        if (page != page_head) {
 316                get_page(page_head);
 317                put_page(page);
 318        }
 319#endif
 320
 321        lock_page(page_head);
 322
 323        /*
 324         * If page_head->mapping is NULL, then it cannot be a PageAnon
 325         * page; but it might be the ZERO_PAGE or in the gate area or
 326         * in a special mapping (all cases which we are happy to fail);
 327         * or it may have been a good file page when get_user_pages_fast
 328         * found it, but truncated or holepunched or subjected to
 329         * invalidate_complete_page2 before we got the page lock (also
 330         * cases which we are happy to fail).  And we hold a reference,
 331         * so refcount care in invalidate_complete_page's remove_mapping
 332         * prevents drop_caches from setting mapping to NULL beneath us.
 333         *
 334         * The case we do have to guard against is when memory pressure made
 335         * shmem_writepage move it from filecache to swapcache beneath us:
 336         * an unlikely race, but we do need to retry for page_head->mapping.
 337         */
 338        if (!page_head->mapping) {
 339                int shmem_swizzled = PageSwapCache(page_head);
 340                unlock_page(page_head);
 341                put_page(page_head);
 342                if (shmem_swizzled)
 343                        goto again;
 344                return -EFAULT;
 345        }
 346
 347        /*
 348         * Private mappings are handled in a simple way.
 349         *
 350         * NOTE: When userspace waits on a MAP_SHARED mapping, even if
 351         * it's a read-only handle, it's expected that futexes attach to
 352         * the object not the particular process.
 353         */
 354        if (PageAnon(page_head)) {
 355                /*
 356                 * A RO anonymous page will never change and thus doesn't make
 357                 * sense for futex operations.
 358                 */
 359                if (ro) {
 360                        err = -EFAULT;
 361                        goto out;
 362                }
 363
 364                key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
 365                key->private.mm = mm;
 366                key->private.address = address;
 367        } else {
 368                key->both.offset |= FUT_OFF_INODE; /* inode-based key */
 369                key->shared.inode = page_head->mapping->host;
 370                key->shared.pgoff = basepage_index(page);
 371        }
 372
 373        get_futex_key_refs(key);
 374
 375out:
 376        unlock_page(page_head);
 377        put_page(page_head);
 378        return err;
 379}
 380
 381static inline void put_futex_key(union futex_key *key)
 382{
 383        drop_futex_key_refs(key);
 384}
 385
 386/**
 387 * fault_in_user_writeable() - Fault in user address and verify RW access
 388 * @uaddr:      pointer to faulting user space address
 389 *
 390 * Slow path to fixup the fault we just took in the atomic write
 391 * access to @uaddr.
 392 *
 393 * We have no generic implementation of a non-destructive write to the
 394 * user address. We know that we faulted in the atomic pagefault
 395 * disabled section so we can as well avoid the #PF overhead by
 396 * calling get_user_pages() right away.
 397 */
 398static int fault_in_user_writeable(u32 __user *uaddr)
 399{
 400        struct mm_struct *mm = current->mm;
 401        int ret;
 402
 403        down_read(&mm->mmap_sem);
 404        ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
 405                               FAULT_FLAG_WRITE);
 406        up_read(&mm->mmap_sem);
 407
 408        return ret < 0 ? ret : 0;
 409}
 410
 411/**
 412 * futex_top_waiter() - Return the highest priority waiter on a futex
 413 * @hb:         the hash bucket the futex_q's reside in
 414 * @key:        the futex key (to distinguish it from other futex futex_q's)
 415 *
 416 * Must be called with the hb lock held.
 417 */
 418static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
 419                                        union futex_key *key)
 420{
 421        struct futex_q *this;
 422
 423        plist_for_each_entry(this, &hb->chain, list) {
 424                if (match_futex(&this->key, key))
 425                        return this;
 426        }
 427        return NULL;
 428}
 429
 430static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
 431                                      u32 uval, u32 newval)
 432{
 433        int ret;
 434
 435        pagefault_disable();
 436        ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
 437        pagefault_enable();
 438
 439        return ret;
 440}
 441
 442static int get_futex_value_locked(u32 *dest, u32 __user *from)
 443{
 444        int ret;
 445
 446        pagefault_disable();
 447        ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
 448        pagefault_enable();
 449
 450        return ret ? -EFAULT : 0;
 451}
 452
 453
 454/*
 455 * PI code:
 456 */
 457static int refill_pi_state_cache(void)
 458{
 459        struct futex_pi_state *pi_state;
 460
 461        if (likely(current->pi_state_cache))
 462                return 0;
 463
 464        pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
 465
 466        if (!pi_state)
 467                return -ENOMEM;
 468
 469        INIT_LIST_HEAD(&pi_state->list);
 470        /* pi_mutex gets initialized later */
 471        pi_state->owner = NULL;
 472        atomic_set(&pi_state->refcount, 1);
 473        pi_state->key = FUTEX_KEY_INIT;
 474
 475        current->pi_state_cache = pi_state;
 476
 477        return 0;
 478}
 479
 480static struct futex_pi_state * alloc_pi_state(void)
 481{
 482        struct futex_pi_state *pi_state = current->pi_state_cache;
 483
 484        WARN_ON(!pi_state);
 485        current->pi_state_cache = NULL;
 486
 487        return pi_state;
 488}
 489
 490static void free_pi_state(struct futex_pi_state *pi_state)
 491{
 492        if (!atomic_dec_and_test(&pi_state->refcount))
 493                return;
 494
 495        /*
 496         * If pi_state->owner is NULL, the owner is most probably dying
 497         * and has cleaned up the pi_state already
 498         */
 499        if (pi_state->owner) {
 500                raw_spin_lock_irq(&pi_state->owner->pi_lock);
 501                list_del_init(&pi_state->list);
 502                raw_spin_unlock_irq(&pi_state->owner->pi_lock);
 503
 504                rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
 505        }
 506
 507        if (current->pi_state_cache)
 508                kfree(pi_state);
 509        else {
 510                /*
 511                 * pi_state->list is already empty.
 512                 * clear pi_state->owner.
 513                 * refcount is at 0 - put it back to 1.
 514                 */
 515                pi_state->owner = NULL;
 516                atomic_set(&pi_state->refcount, 1);
 517                current->pi_state_cache = pi_state;
 518        }
 519}
 520
 521/*
 522 * Look up the task based on what TID userspace gave us.
 523 * We dont trust it.
 524 */
 525static struct task_struct * futex_find_get_task(pid_t pid)
 526{
 527        struct task_struct *p;
 528
 529        rcu_read_lock();
 530        p = find_task_by_vpid(pid);
 531        if (p)
 532                get_task_struct(p);
 533
 534        rcu_read_unlock();
 535
 536        return p;
 537}
 538
 539/*
 540 * This task is holding PI mutexes at exit time => bad.
 541 * Kernel cleans up PI-state, but userspace is likely hosed.
 542 * (Robust-futex cleanup is separate and might save the day for userspace.)
 543 */
 544void exit_pi_state_list(struct task_struct *curr)
 545{
 546        struct list_head *next, *head = &curr->pi_state_list;
 547        struct futex_pi_state *pi_state;
 548        struct futex_hash_bucket *hb;
 549        union futex_key key = FUTEX_KEY_INIT;
 550
 551        if (!futex_cmpxchg_enabled)
 552                return;
 553        /*
 554         * We are a ZOMBIE and nobody can enqueue itself on
 555         * pi_state_list anymore, but we have to be careful
 556         * versus waiters unqueueing themselves:
 557         */
 558        raw_spin_lock_irq(&curr->pi_lock);
 559        while (!list_empty(head)) {
 560
 561                next = head->next;
 562                pi_state = list_entry(next, struct futex_pi_state, list);
 563                key = pi_state->key;
 564                hb = hash_futex(&key);
 565                raw_spin_unlock_irq(&curr->pi_lock);
 566
 567                spin_lock(&hb->lock);
 568
 569                raw_spin_lock_irq(&curr->pi_lock);
 570                /*
 571                 * We dropped the pi-lock, so re-check whether this
 572                 * task still owns the PI-state:
 573                 */
 574                if (head->next != next) {
 575                        spin_unlock(&hb->lock);
 576                        continue;
 577                }
 578
 579                WARN_ON(pi_state->owner != curr);
 580                WARN_ON(list_empty(&pi_state->list));
 581                list_del_init(&pi_state->list);
 582                pi_state->owner = NULL;
 583                raw_spin_unlock_irq(&curr->pi_lock);
 584
 585                rt_mutex_unlock(&pi_state->pi_mutex);
 586
 587                spin_unlock(&hb->lock);
 588
 589                raw_spin_lock_irq(&curr->pi_lock);
 590        }
 591        raw_spin_unlock_irq(&curr->pi_lock);
 592}
 593
 594static int
 595lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 596                union futex_key *key, struct futex_pi_state **ps)
 597{
 598        struct futex_pi_state *pi_state = NULL;
 599        struct futex_q *this, *next;
 600        struct plist_head *head;
 601        struct task_struct *p;
 602        pid_t pid = uval & FUTEX_TID_MASK;
 603
 604        head = &hb->chain;
 605
 606        plist_for_each_entry_safe(this, next, head, list) {
 607                if (match_futex(&this->key, key)) {
 608                        /*
 609                         * Another waiter already exists - bump up
 610                         * the refcount and return its pi_state:
 611                         */
 612                        pi_state = this->pi_state;
 613                        /*
 614                         * Userspace might have messed up non-PI and PI futexes
 615                         */
 616                        if (unlikely(!pi_state))
 617                                return -EINVAL;
 618
 619                        WARN_ON(!atomic_read(&pi_state->refcount));
 620
 621                        /*
 622                         * When pi_state->owner is NULL then the owner died
 623                         * and another waiter is on the fly. pi_state->owner
 624                         * is fixed up by the task which acquires
 625                         * pi_state->rt_mutex.
 626                         *
 627                         * We do not check for pid == 0 which can happen when
 628                         * the owner died and robust_list_exit() cleared the
 629                         * TID.
 630                         */
 631                        if (pid && pi_state->owner) {
 632                                /*
 633                                 * Bail out if user space manipulated the
 634                                 * futex value.
 635                                 */
 636                                if (pid != task_pid_vnr(pi_state->owner))
 637                                        return -EINVAL;
 638                        }
 639
 640                        atomic_inc(&pi_state->refcount);
 641                        *ps = pi_state;
 642
 643                        return 0;
 644                }
 645        }
 646
 647        /*
 648         * We are the first waiter - try to look up the real owner and attach
 649         * the new pi_state to it, but bail out when TID = 0
 650         */
 651        if (!pid)
 652                return -ESRCH;
 653        p = futex_find_get_task(pid);
 654        if (!p)
 655                return -ESRCH;
 656
 657        /*
 658         * We need to look at the task state flags to figure out,
 659         * whether the task is exiting. To protect against the do_exit
 660         * change of the task flags, we do this protected by
 661         * p->pi_lock:
 662         */
 663        raw_spin_lock_irq(&p->pi_lock);
 664        if (unlikely(p->flags & PF_EXITING)) {
 665                /*
 666                 * The task is on the way out. When PF_EXITPIDONE is
 667                 * set, we know that the task has finished the
 668                 * cleanup:
 669                 */
 670                int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
 671
 672                raw_spin_unlock_irq(&p->pi_lock);
 673                put_task_struct(p);
 674                return ret;
 675        }
 676
 677        pi_state = alloc_pi_state();
 678
 679        /*
 680         * Initialize the pi_mutex in locked state and make 'p'
 681         * the owner of it:
 682         */
 683        rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 684
 685        /* Store the key for possible exit cleanups: */
 686        pi_state->key = *key;
 687
 688        WARN_ON(!list_empty(&pi_state->list));
 689        list_add(&pi_state->list, &p->pi_state_list);
 690        pi_state->owner = p;
 691        raw_spin_unlock_irq(&p->pi_lock);
 692
 693        put_task_struct(p);
 694
 695        *ps = pi_state;
 696
 697        return 0;
 698}
 699
 700/**
 701 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
 702 * @uaddr:              the pi futex user address
 703 * @hb:                 the pi futex hash bucket
 704 * @key:                the futex key associated with uaddr and hb
 705 * @ps:                 the pi_state pointer where we store the result of the
 706 *                      lookup
 707 * @task:               the task to perform the atomic lock work for.  This will
 708 *                      be "current" except in the case of requeue pi.
 709 * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
 710 *
 711 * Return:
 712 *  0 - ready to wait;
 713 *  1 - acquired the lock;
 714 * <0 - error
 715 *
 716 * The hb->lock and futex_key refs shall be held by the caller.
 717 */
 718static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
 719                                union futex_key *key,
 720                                struct futex_pi_state **ps,
 721                                struct task_struct *task, int set_waiters)
 722{
 723        int lock_taken, ret, force_take = 0;
 724        u32 uval, newval, curval, vpid = task_pid_vnr(task);
 725
 726retry:
 727        ret = lock_taken = 0;
 728
 729        /*
 730         * To avoid races, we attempt to take the lock here again
 731         * (by doing a 0 -> TID atomic cmpxchg), while holding all
 732         * the locks. It will most likely not succeed.
 733         */
 734        newval = vpid;
 735        if (set_waiters)
 736                newval |= FUTEX_WAITERS;
 737
 738        if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
 739                return -EFAULT;
 740
 741        /*
 742         * Detect deadlocks.
 743         */
 744        if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
 745                return -EDEADLK;
 746
 747        /*
 748         * Surprise - we got the lock. Just return to userspace:
 749         */
 750        if (unlikely(!curval))
 751                return 1;
 752
 753        uval = curval;
 754
 755        /*
 756         * Set the FUTEX_WAITERS flag, so the owner will know it has someone
 757         * to wake at the next unlock.
 758         */
 759        newval = curval | FUTEX_WAITERS;
 760
 761        /*
 762         * Should we force take the futex? See below.
 763         */
 764        if (unlikely(force_take)) {
 765                /*
 766                 * Keep the OWNER_DIED and the WAITERS bit and set the
 767                 * new TID value.
 768                 */
 769                newval = (curval & ~FUTEX_TID_MASK) | vpid;
 770                force_take = 0;
 771                lock_taken = 1;
 772        }
 773
 774        if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
 775                return -EFAULT;
 776        if (unlikely(curval != uval))
 777                goto retry;
 778
 779        /*
 780         * We took the lock due to forced take over.
 781         */
 782        if (unlikely(lock_taken))
 783                return 1;
 784
 785        /*
 786         * We dont have the lock. Look up the PI state (or create it if
 787         * we are the first waiter):
 788         */
 789        ret = lookup_pi_state(uval, hb, key, ps);
 790
 791        if (unlikely(ret)) {
 792                switch (ret) {
 793                case -ESRCH:
 794                        /*
 795                         * We failed to find an owner for this
 796                         * futex. So we have no pi_state to block
 797                         * on. This can happen in two cases:
 798                         *
 799                         * 1) The owner died
 800                         * 2) A stale FUTEX_WAITERS bit
 801                         *
 802                         * Re-read the futex value.
 803                         */
 804                        if (get_futex_value_locked(&curval, uaddr))
 805                                return -EFAULT;
 806
 807                        /*
 808                         * If the owner died or we have a stale
 809                         * WAITERS bit the owner TID in the user space
 810                         * futex is 0.
 811                         */
 812                        if (!(curval & FUTEX_TID_MASK)) {
 813                                force_take = 1;
 814                                goto retry;
 815                        }
 816                default:
 817                        break;
 818                }
 819        }
 820
 821        return ret;
 822}
 823
 824/**
 825 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
 826 * @q:  The futex_q to unqueue
 827 *
 828 * The q->lock_ptr must not be NULL and must be held by the caller.
 829 */
 830static void __unqueue_futex(struct futex_q *q)
 831{
 832        struct futex_hash_bucket *hb;
 833
 834        if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
 835            || WARN_ON(plist_node_empty(&q->list)))
 836                return;
 837
 838        hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
 839        plist_del(&q->list, &hb->chain);
 840}
 841
 842/*
 843 * The hash bucket lock must be held when this is called.
 844 * Afterwards, the futex_q must not be accessed.
 845 */
 846static void wake_futex(struct futex_q *q)
 847{
 848        struct task_struct *p = q->task;
 849
 850        if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
 851                return;
 852
 853        /*
 854         * We set q->lock_ptr = NULL _before_ we wake up the task. If
 855         * a non-futex wake up happens on another CPU then the task
 856         * might exit and p would dereference a non-existing task
 857         * struct. Prevent this by holding a reference on p across the
 858         * wake up.
 859         */
 860        get_task_struct(p);
 861
 862        __unqueue_futex(q);
 863        /*
 864         * The waiting task can free the futex_q as soon as
 865         * q->lock_ptr = NULL is written, without taking any locks. A
 866         * memory barrier is required here to prevent the following
 867         * store to lock_ptr from getting ahead of the plist_del.
 868         */
 869        smp_wmb();
 870        q->lock_ptr = NULL;
 871
 872        wake_up_state(p, TASK_NORMAL);
 873        put_task_struct(p);
 874}
 875
 876static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
 877{
 878        struct task_struct *new_owner;
 879        struct futex_pi_state *pi_state = this->pi_state;
 880        u32 uninitialized_var(curval), newval;
 881
 882        if (!pi_state)
 883                return -EINVAL;
 884
 885        /*
 886         * If current does not own the pi_state then the futex is
 887         * inconsistent and user space fiddled with the futex value.
 888         */
 889        if (pi_state->owner != current)
 890                return -EINVAL;
 891
 892        raw_spin_lock(&pi_state->pi_mutex.wait_lock);
 893        new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
 894
 895        /*
 896         * It is possible that the next waiter (the one that brought
 897         * this owner to the kernel) timed out and is no longer
 898         * waiting on the lock.
 899         */
 900        if (!new_owner)
 901                new_owner = this->task;
 902
 903        /*
 904         * We pass it to the next owner. (The WAITERS bit is always
 905         * kept enabled while there is PI state around. We must also
 906         * preserve the owner died bit.)
 907         */
 908        if (!(uval & FUTEX_OWNER_DIED)) {
 909                int ret = 0;
 910
 911                newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
 912
 913                if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
 914                        ret = -EFAULT;
 915                else if (curval != uval)
 916                        ret = -EINVAL;
 917                if (ret) {
 918                        raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
 919                        return ret;
 920                }
 921        }
 922
 923        raw_spin_lock_irq(&pi_state->owner->pi_lock);
 924        WARN_ON(list_empty(&pi_state->list));
 925        list_del_init(&pi_state->list);
 926        raw_spin_unlock_irq(&pi_state->owner->pi_lock);
 927
 928        raw_spin_lock_irq(&new_owner->pi_lock);
 929        WARN_ON(!list_empty(&pi_state->list));
 930        list_add(&pi_state->list, &new_owner->pi_state_list);
 931        pi_state->owner = new_owner;
 932        raw_spin_unlock_irq(&new_owner->pi_lock);
 933
 934        raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
 935        rt_mutex_unlock(&pi_state->pi_mutex);
 936
 937        return 0;
 938}
 939
 940static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
 941{
 942        u32 uninitialized_var(oldval);
 943
 944        /*
 945         * There is no waiter, so we unlock the futex. The owner died
 946         * bit has not to be preserved here. We are the owner:
 947         */
 948        if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
 949                return -EFAULT;
 950        if (oldval != uval)
 951                return -EAGAIN;
 952
 953        return 0;
 954}
 955
 956/*
 957 * Express the locking dependencies for lockdep:
 958 */
 959static inline void
 960double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 961{
 962        if (hb1 <= hb2) {
 963                spin_lock(&hb1->lock);
 964                if (hb1 < hb2)
 965                        spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
 966        } else { /* hb1 > hb2 */
 967                spin_lock(&hb2->lock);
 968                spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
 969        }
 970}
 971
 972static inline void
 973double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 974{
 975        spin_unlock(&hb1->lock);
 976        if (hb1 != hb2)
 977                spin_unlock(&hb2->lock);
 978}
 979
 980/*
 981 * Wake up waiters matching bitset queued on this futex (uaddr).
 982 */
 983static int
 984futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
 985{
 986        struct futex_hash_bucket *hb;
 987        struct futex_q *this, *next;
 988        struct plist_head *head;
 989        union futex_key key = FUTEX_KEY_INIT;
 990        int ret;
 991
 992        if (!bitset)
 993                return -EINVAL;
 994
 995        ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
 996        if (unlikely(ret != 0))
 997                goto out;
 998
 999        hb = hash_futex(&key);
1000        spin_lock(&hb->lock);
1001        head = &hb->chain;
1002
1003        plist_for_each_entry_safe(this, next, head, list) {
1004                if (match_futex (&this->key, &key)) {
1005                        if (this->pi_state || this->rt_waiter) {
1006                                ret = -EINVAL;
1007                                break;
1008                        }
1009
1010                        /* Check if one of the bits is set in both bitsets */
1011                        if (!(this->bitset & bitset))
1012                                continue;
1013
1014                        wake_futex(this);
1015                        if (++ret >= nr_wake)
1016                                break;
1017                }
1018        }
1019
1020        spin_unlock(&hb->lock);
1021        put_futex_key(&key);
1022out:
1023        return ret;
1024}
1025
1026/*
1027 * Wake up all waiters hashed on the physical page that is mapped
1028 * to this virtual address:
1029 */
1030static int
1031futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1032              int nr_wake, int nr_wake2, int op)
1033{
1034        union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1035        struct futex_hash_bucket *hb1, *hb2;
1036        struct plist_head *head;
1037        struct futex_q *this, *next;
1038        int ret, op_ret;
1039
1040retry:
1041        ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1042        if (unlikely(ret != 0))
1043                goto out;
1044        ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1045        if (unlikely(ret != 0))
1046                goto out_put_key1;
1047
1048        hb1 = hash_futex(&key1);
1049        hb2 = hash_futex(&key2);
1050
1051retry_private:
1052        double_lock_hb(hb1, hb2);
1053        op_ret = futex_atomic_op_inuser(op, uaddr2);
1054        if (unlikely(op_ret < 0)) {
1055
1056                double_unlock_hb(hb1, hb2);
1057
1058#ifndef CONFIG_MMU
1059                /*
1060                 * we don't get EFAULT from MMU faults if we don't have an MMU,
1061                 * but we might get them from range checking
1062                 */
1063                ret = op_ret;
1064                goto out_put_keys;
1065#endif
1066
1067                if (unlikely(op_ret != -EFAULT)) {
1068                        ret = op_ret;
1069                        goto out_put_keys;
1070                }
1071
1072                ret = fault_in_user_writeable(uaddr2);
1073                if (ret)
1074                        goto out_put_keys;
1075
1076                if (!(flags & FLAGS_SHARED))
1077                        goto retry_private;
1078
1079                put_futex_key(&key2);
1080                put_futex_key(&key1);
1081                goto retry;
1082        }
1083
1084        head = &hb1->chain;
1085
1086        plist_for_each_entry_safe(this, next, head, list) {
1087                if (match_futex (&this->key, &key1)) {
1088                        if (this->pi_state || this->rt_waiter) {
1089                                ret = -EINVAL;
1090                                goto out_unlock;
1091                        }
1092                        wake_futex(this);
1093                        if (++ret >= nr_wake)
1094                                break;
1095                }
1096        }
1097
1098        if (op_ret > 0) {
1099                head = &hb2->chain;
1100
1101                op_ret = 0;
1102                plist_for_each_entry_safe(this, next, head, list) {
1103                        if (match_futex (&this->key, &key2)) {
1104                                if (this->pi_state || this->rt_waiter) {
1105                                        ret = -EINVAL;
1106                                        goto out_unlock;
1107                                }
1108                                wake_futex(this);
1109                                if (++op_ret >= nr_wake2)
1110                                        break;
1111                        }
1112                }
1113                ret += op_ret;
1114        }
1115
1116out_unlock:
1117        double_unlock_hb(hb1, hb2);
1118out_put_keys:
1119        put_futex_key(&key2);
1120out_put_key1:
1121        put_futex_key(&key1);
1122out:
1123        return ret;
1124}
1125
1126/**
1127 * requeue_futex() - Requeue a futex_q from one hb to another
1128 * @q:          the futex_q to requeue
1129 * @hb1:        the source hash_bucket
1130 * @hb2:        the target hash_bucket
1131 * @key2:       the new key for the requeued futex_q
1132 */
1133static inline
1134void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1135                   struct futex_hash_bucket *hb2, union futex_key *key2)
1136{
1137
1138        /*
1139         * If key1 and key2 hash to the same bucket, no need to
1140         * requeue.
1141         */
1142        if (likely(&hb1->chain != &hb2->chain)) {
1143                plist_del(&q->list, &hb1->chain);
1144                plist_add(&q->list, &hb2->chain);
1145                q->lock_ptr = &hb2->lock;
1146        }
1147        get_futex_key_refs(key2);
1148        q->key = *key2;
1149}
1150
1151/**
1152 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1153 * @q:          the futex_q
1154 * @key:        the key of the requeue target futex
1155 * @hb:         the hash_bucket of the requeue target futex
1156 *
1157 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1158 * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1159 * to the requeue target futex so the waiter can detect the wakeup on the right
1160 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1161 * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1162 * to protect access to the pi_state to fixup the owner later.  Must be called
1163 * with both q->lock_ptr and hb->lock held.
1164 */
1165static inline
1166void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1167                           struct futex_hash_bucket *hb)
1168{
1169        get_futex_key_refs(key);
1170        q->key = *key;
1171
1172        __unqueue_futex(q);
1173
1174        WARN_ON(!q->rt_waiter);
1175        q->rt_waiter = NULL;
1176
1177        q->lock_ptr = &hb->lock;
1178
1179        wake_up_state(q->task, TASK_NORMAL);
1180}
1181
1182/**
1183 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1184 * @pifutex:            the user address of the to futex
1185 * @hb1:                the from futex hash bucket, must be locked by the caller
1186 * @hb2:                the to futex hash bucket, must be locked by the caller
1187 * @key1:               the from futex key
1188 * @key2:               the to futex key
1189 * @ps:                 address to store the pi_state pointer
1190 * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1191 *
1192 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1193 * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1194 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1195 * hb1 and hb2 must be held by the caller.
1196 *
1197 * Return:
1198 *  0 - failed to acquire the lock atomically;
1199 *  1 - acquired the lock;
1200 * <0 - error
1201 */
1202static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1203                                 struct futex_hash_bucket *hb1,
1204                                 struct futex_hash_bucket *hb2,
1205                                 union futex_key *key1, union futex_key *key2,
1206                                 struct futex_pi_state **ps, int set_waiters)
1207{
1208        struct futex_q *top_waiter = NULL;
1209        u32 curval;
1210        int ret;
1211
1212        if (get_futex_value_locked(&curval, pifutex))
1213                return -EFAULT;
1214
1215        /*
1216         * Find the top_waiter and determine if there are additional waiters.
1217         * If the caller intends to requeue more than 1 waiter to pifutex,
1218         * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1219         * as we have means to handle the possible fault.  If not, don't set
1220         * the bit unecessarily as it will force the subsequent unlock to enter
1221         * the kernel.
1222         */
1223        top_waiter = futex_top_waiter(hb1, key1);
1224
1225        /* There are no waiters, nothing for us to do. */
1226        if (!top_waiter)
1227                return 0;
1228
1229        /* Ensure we requeue to the expected futex. */
1230        if (!match_futex(top_waiter->requeue_pi_key, key2))
1231                return -EINVAL;
1232
1233        /*
1234         * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1235         * the contended case or if set_waiters is 1.  The pi_state is returned
1236         * in ps in contended cases.
1237         */
1238        ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1239                                   set_waiters);
1240        if (ret == 1)
1241                requeue_pi_wake_futex(top_waiter, key2, hb2);
1242
1243        return ret;
1244}
1245
1246/**
1247 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1248 * @uaddr1:     source futex user address
1249 * @flags:      futex flags (FLAGS_SHARED, etc.)
1250 * @uaddr2:     target futex user address
1251 * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1252 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1253 * @cmpval:     @uaddr1 expected value (or %NULL)
1254 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1255 *              pi futex (pi to pi requeue is not supported)
1256 *
1257 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1258 * uaddr2 atomically on behalf of the top waiter.
1259 *
1260 * Return:
1261 * >=0 - on success, the number of tasks requeued or woken;
1262 *  <0 - on error
1263 */
1264static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1265                         u32 __user *uaddr2, int nr_wake, int nr_requeue,
1266                         u32 *cmpval, int requeue_pi)
1267{
1268        union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1269        int drop_count = 0, task_count = 0, ret;
1270        struct futex_pi_state *pi_state = NULL;
1271        struct futex_hash_bucket *hb1, *hb2;
1272        struct plist_head *head1;
1273        struct futex_q *this, *next;
1274        u32 curval2;
1275
1276        if (requeue_pi) {
1277                /*
1278                 * requeue_pi requires a pi_state, try to allocate it now
1279                 * without any locks in case it fails.
1280                 */
1281                if (refill_pi_state_cache())
1282                        return -ENOMEM;
1283                /*
1284                 * requeue_pi must wake as many tasks as it can, up to nr_wake
1285                 * + nr_requeue, since it acquires the rt_mutex prior to
1286                 * returning to userspace, so as to not leave the rt_mutex with
1287                 * waiters and no owner.  However, second and third wake-ups
1288                 * cannot be predicted as they involve race conditions with the
1289                 * first wake and a fault while looking up the pi_state.  Both
1290                 * pthread_cond_signal() and pthread_cond_broadcast() should
1291                 * use nr_wake=1.
1292                 */
1293                if (nr_wake != 1)
1294                        return -EINVAL;
1295        }
1296
1297retry:
1298        if (pi_state != NULL) {
1299                /*
1300                 * We will have to lookup the pi_state again, so free this one
1301                 * to keep the accounting correct.
1302                 */
1303                free_pi_state(pi_state);
1304                pi_state = NULL;
1305        }
1306
1307        ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1308        if (unlikely(ret != 0))
1309                goto out;
1310        ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1311                            requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1312        if (unlikely(ret != 0))
1313                goto out_put_key1;
1314
1315        hb1 = hash_futex(&key1);
1316        hb2 = hash_futex(&key2);
1317
1318retry_private:
1319        double_lock_hb(hb1, hb2);
1320
1321        if (likely(cmpval != NULL)) {
1322                u32 curval;
1323
1324                ret = get_futex_value_locked(&curval, uaddr1);
1325
1326                if (unlikely(ret)) {
1327                        double_unlock_hb(hb1, hb2);
1328
1329                        ret = get_user(curval, uaddr1);
1330                        if (ret)
1331                                goto out_put_keys;
1332
1333                        if (!(flags & FLAGS_SHARED))
1334                                goto retry_private;
1335
1336                        put_futex_key(&key2);
1337                        put_futex_key(&key1);
1338                        goto retry;
1339                }
1340                if (curval != *cmpval) {
1341                        ret = -EAGAIN;
1342                        goto out_unlock;
1343                }
1344        }
1345
1346        if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1347                /*
1348                 * Attempt to acquire uaddr2 and wake the top waiter. If we
1349                 * intend to requeue waiters, force setting the FUTEX_WAITERS
1350                 * bit.  We force this here where we are able to easily handle
1351                 * faults rather in the requeue loop below.
1352                 */
1353                ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1354                                                 &key2, &pi_state, nr_requeue);
1355
1356                /*
1357                 * At this point the top_waiter has either taken uaddr2 or is
1358                 * waiting on it.  If the former, then the pi_state will not
1359                 * exist yet, look it up one more time to ensure we have a
1360                 * reference to it.
1361                 */
1362                if (ret == 1) {
1363                        WARN_ON(pi_state);
1364                        drop_count++;
1365                        task_count++;
1366                        ret = get_futex_value_locked(&curval2, uaddr2);
1367                        if (!ret)
1368                                ret = lookup_pi_state(curval2, hb2, &key2,
1369                                                      &pi_state);
1370                }
1371
1372                switch (ret) {
1373                case 0:
1374                        break;
1375                case -EFAULT:
1376                        double_unlock_hb(hb1, hb2);
1377                        put_futex_key(&key2);
1378                        put_futex_key(&key1);
1379                        ret = fault_in_user_writeable(uaddr2);
1380                        if (!ret)
1381                                goto retry;
1382                        goto out;
1383                case -EAGAIN:
1384                        /* The owner was exiting, try again. */
1385                        double_unlock_hb(hb1, hb2);
1386                        put_futex_key(&key2);
1387                        put_futex_key(&key1);
1388                        cond_resched();
1389                        goto retry;
1390                default:
1391                        goto out_unlock;
1392                }
1393        }
1394
1395        head1 = &hb1->chain;
1396        plist_for_each_entry_safe(this, next, head1, list) {
1397                if (task_count - nr_wake >= nr_requeue)
1398                        break;
1399
1400                if (!match_futex(&this->key, &key1))
1401                        continue;
1402
1403                /*
1404                 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1405                 * be paired with each other and no other futex ops.
1406                 *
1407                 * We should never be requeueing a futex_q with a pi_state,
1408                 * which is awaiting a futex_unlock_pi().
1409                 */
1410                if ((requeue_pi && !this->rt_waiter) ||
1411                    (!requeue_pi && this->rt_waiter) ||
1412                    this->pi_state) {
1413                        ret = -EINVAL;
1414                        break;
1415                }
1416
1417                /*
1418                 * Wake nr_wake waiters.  For requeue_pi, if we acquired the
1419                 * lock, we already woke the top_waiter.  If not, it will be
1420                 * woken by futex_unlock_pi().
1421                 */
1422                if (++task_count <= nr_wake && !requeue_pi) {
1423                        wake_futex(this);
1424                        continue;
1425                }
1426
1427                /* Ensure we requeue to the expected futex for requeue_pi. */
1428                if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1429                        ret = -EINVAL;
1430                        break;
1431                }
1432
1433                /*
1434                 * Requeue nr_requeue waiters and possibly one more in the case
1435                 * of requeue_pi if we couldn't acquire the lock atomically.
1436                 */
1437                if (requeue_pi) {
1438                        /* Prepare the waiter to take the rt_mutex. */
1439                        atomic_inc(&pi_state->refcount);
1440                        this->pi_state = pi_state;
1441                        ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1442                                                        this->rt_waiter,
1443                                                        this->task, 1);
1444                        if (ret == 1) {
1445                                /* We got the lock. */
1446                                requeue_pi_wake_futex(this, &key2, hb2);
1447                                drop_count++;
1448                                continue;
1449                        } else if (ret) {
1450                                /* -EDEADLK */
1451                                this->pi_state = NULL;
1452                                free_pi_state(pi_state);
1453                                goto out_unlock;
1454                        }
1455                }
1456                requeue_futex(this, hb1, hb2, &key2);
1457                drop_count++;
1458        }
1459
1460out_unlock:
1461        double_unlock_hb(hb1, hb2);
1462
1463        /*
1464         * drop_futex_key_refs() must be called outside the spinlocks. During
1465         * the requeue we moved futex_q's from the hash bucket at key1 to the
1466         * one at key2 and updated their key pointer.  We no longer need to
1467         * hold the references to key1.
1468         */
1469        while (--drop_count >= 0)
1470                drop_futex_key_refs(&key1);
1471
1472out_put_keys:
1473        put_futex_key(&key2);
1474out_put_key1:
1475        put_futex_key(&key1);
1476out:
1477        if (pi_state != NULL)
1478                free_pi_state(pi_state);
1479        return ret ? ret : task_count;
1480}
1481
1482/* The key must be already stored in q->key. */
1483static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1484        __acquires(&hb->lock)
1485{
1486        struct futex_hash_bucket *hb;
1487
1488        hb = hash_futex(&q->key);
1489        q->lock_ptr = &hb->lock;
1490
1491        spin_lock(&hb->lock);
1492        return hb;
1493}
1494
1495static inline void
1496queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1497        __releases(&hb->lock)
1498{
1499        spin_unlock(&hb->lock);
1500}
1501
1502/**
1503 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1504 * @q:  The futex_q to enqueue
1505 * @hb: The destination hash bucket
1506 *
1507 * The hb->lock must be held by the caller, and is released here. A call to
1508 * queue_me() is typically paired with exactly one call to unqueue_me().  The
1509 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1510 * or nothing if the unqueue is done as part of the wake process and the unqueue
1511 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1512 * an example).
1513 */
1514static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1515        __releases(&hb->lock)
1516{
1517        int prio;
1518
1519        /*
1520         * The priority used to register this element is
1521         * - either the real thread-priority for the real-time threads
1522         * (i.e. threads with a priority lower than MAX_RT_PRIO)
1523         * - or MAX_RT_PRIO for non-RT threads.
1524         * Thus, all RT-threads are woken first in priority order, and
1525         * the others are woken last, in FIFO order.
1526         */
1527        prio = min(current->normal_prio, MAX_RT_PRIO);
1528
1529        plist_node_init(&q->list, prio);
1530        plist_add(&q->list, &hb->chain);
1531        q->task = current;
1532        spin_unlock(&hb->lock);
1533}
1534
1535/**
1536 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1537 * @q:  The futex_q to unqueue
1538 *
1539 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1540 * be paired with exactly one earlier call to queue_me().
1541 *
1542 * Return:
1543 *   1 - if the futex_q was still queued (and we removed unqueued it);
1544 *   0 - if the futex_q was already removed by the waking thread
1545 */
1546static int unqueue_me(struct futex_q *q)
1547{
1548        spinlock_t *lock_ptr;
1549        int ret = 0;
1550
1551        /* In the common case we don't take the spinlock, which is nice. */
1552retry:
1553        lock_ptr = q->lock_ptr;
1554        barrier();
1555        if (lock_ptr != NULL) {
1556                spin_lock(lock_ptr);
1557                /*
1558                 * q->lock_ptr can change between reading it and
1559                 * spin_lock(), causing us to take the wrong lock.  This
1560                 * corrects the race condition.
1561                 *
1562                 * Reasoning goes like this: if we have the wrong lock,
1563                 * q->lock_ptr must have changed (maybe several times)
1564                 * between reading it and the spin_lock().  It can
1565                 * change again after the spin_lock() but only if it was
1566                 * already changed before the spin_lock().  It cannot,
1567                 * however, change back to the original value.  Therefore
1568                 * we can detect whether we acquired the correct lock.
1569                 */
1570                if (unlikely(lock_ptr != q->lock_ptr)) {
1571                        spin_unlock(lock_ptr);
1572                        goto retry;
1573                }
1574                __unqueue_futex(q);
1575
1576                BUG_ON(q->pi_state);
1577
1578                spin_unlock(lock_ptr);
1579                ret = 1;
1580        }
1581
1582        drop_futex_key_refs(&q->key);
1583        return ret;
1584}
1585
1586/*
1587 * PI futexes can not be requeued and must remove themself from the
1588 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1589 * and dropped here.
1590 */
1591static void unqueue_me_pi(struct futex_q *q)
1592        __releases(q->lock_ptr)
1593{
1594        __unqueue_futex(q);
1595
1596        BUG_ON(!q->pi_state);
1597        free_pi_state(q->pi_state);
1598        q->pi_state = NULL;
1599
1600        spin_unlock(q->lock_ptr);
1601}
1602
1603/*
1604 * Fixup the pi_state owner with the new owner.
1605 *
1606 * Must be called with hash bucket lock held and mm->sem held for non
1607 * private futexes.
1608 */
1609static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1610                                struct task_struct *newowner)
1611{
1612        u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1613        struct futex_pi_state *pi_state = q->pi_state;
1614        struct task_struct *oldowner = pi_state->owner;
1615        u32 uval, uninitialized_var(curval), newval;
1616        int ret;
1617
1618        /* Owner died? */
1619        if (!pi_state->owner)
1620                newtid |= FUTEX_OWNER_DIED;
1621
1622        /*
1623         * We are here either because we stole the rtmutex from the
1624         * previous highest priority waiter or we are the highest priority
1625         * waiter but failed to get the rtmutex the first time.
1626         * We have to replace the newowner TID in the user space variable.
1627         * This must be atomic as we have to preserve the owner died bit here.
1628         *
1629         * Note: We write the user space value _before_ changing the pi_state
1630         * because we can fault here. Imagine swapped out pages or a fork
1631         * that marked all the anonymous memory readonly for cow.
1632         *
1633         * Modifying pi_state _before_ the user space value would
1634         * leave the pi_state in an inconsistent state when we fault
1635         * here, because we need to drop the hash bucket lock to
1636         * handle the fault. This might be observed in the PID check
1637         * in lookup_pi_state.
1638         */
1639retry:
1640        if (get_futex_value_locked(&uval, uaddr))
1641                goto handle_fault;
1642
1643        while (1) {
1644                newval = (uval & FUTEX_OWNER_DIED) | newtid;
1645
1646                if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1647                        goto handle_fault;
1648                if (curval == uval)
1649                        break;
1650                uval = curval;
1651        }
1652
1653        /*
1654         * We fixed up user space. Now we need to fix the pi_state
1655         * itself.
1656         */
1657        if (pi_state->owner != NULL) {
1658                raw_spin_lock_irq(&pi_state->owner->pi_lock);
1659                WARN_ON(list_empty(&pi_state->list));
1660                list_del_init(&pi_state->list);
1661                raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1662        }
1663
1664        pi_state->owner = newowner;
1665
1666        raw_spin_lock_irq(&newowner->pi_lock);
1667        WARN_ON(!list_empty(&pi_state->list));
1668        list_add(&pi_state->list, &newowner->pi_state_list);
1669        raw_spin_unlock_irq(&newowner->pi_lock);
1670        return 0;
1671
1672        /*
1673         * To handle the page fault we need to drop the hash bucket
1674         * lock here. That gives the other task (either the highest priority
1675         * waiter itself or the task which stole the rtmutex) the
1676         * chance to try the fixup of the pi_state. So once we are
1677         * back from handling the fault we need to check the pi_state
1678         * after reacquiring the hash bucket lock and before trying to
1679         * do another fixup. When the fixup has been done already we
1680         * simply return.
1681         */
1682handle_fault:
1683        spin_unlock(q->lock_ptr);
1684
1685        ret = fault_in_user_writeable(uaddr);
1686
1687        spin_lock(q->lock_ptr);
1688
1689        /*
1690         * Check if someone else fixed it for us:
1691         */
1692        if (pi_state->owner != oldowner)
1693                return 0;
1694
1695        if (ret)
1696                return ret;
1697
1698        goto retry;
1699}
1700
1701static long futex_wait_restart(struct restart_block *restart);
1702
1703/**
1704 * fixup_owner() - Post lock pi_state and corner case management
1705 * @uaddr:      user address of the futex
1706 * @q:          futex_q (contains pi_state and access to the rt_mutex)
1707 * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
1708 *
1709 * After attempting to lock an rt_mutex, this function is called to cleanup
1710 * the pi_state owner as well as handle race conditions that may allow us to
1711 * acquire the lock. Must be called with the hb lock held.
1712 *
1713 * Return:
1714 *  1 - success, lock taken;
1715 *  0 - success, lock not taken;
1716 * <0 - on error (-EFAULT)
1717 */
1718static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1719{
1720        struct task_struct *owner;
1721        int ret = 0;
1722
1723        if (locked) {
1724                /*
1725                 * Got the lock. We might not be the anticipated owner if we
1726                 * did a lock-steal - fix up the PI-state in that case:
1727                 */
1728                if (q->pi_state->owner != current)
1729                        ret = fixup_pi_state_owner(uaddr, q, current);
1730                goto out;
1731        }
1732
1733        /*
1734         * Catch the rare case, where the lock was released when we were on the
1735         * way back before we locked the hash bucket.
1736         */
1737        if (q->pi_state->owner == current) {
1738                /*
1739                 * Try to get the rt_mutex now. This might fail as some other
1740                 * task acquired the rt_mutex after we removed ourself from the
1741                 * rt_mutex waiters list.
1742                 */
1743                if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1744                        locked = 1;
1745                        goto out;
1746                }
1747
1748                /*
1749                 * pi_state is incorrect, some other task did a lock steal and
1750                 * we returned due to timeout or signal without taking the
1751                 * rt_mutex. Too late.
1752                 */
1753                raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1754                owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1755                if (!owner)
1756                        owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1757                raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1758                ret = fixup_pi_state_owner(uaddr, q, owner);
1759                goto out;
1760        }
1761
1762        /*
1763         * Paranoia check. If we did not take the lock, then we should not be
1764         * the owner of the rt_mutex.
1765         */
1766        if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1767                printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1768                                "pi-state %p\n", ret,
1769                                q->pi_state->pi_mutex.owner,
1770                                q->pi_state->owner);
1771
1772out:
1773        return ret ? ret : locked;
1774}
1775
1776/**
1777 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1778 * @hb:         the futex hash bucket, must be locked by the caller
1779 * @q:          the futex_q to queue up on
1780 * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
1781 */
1782static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1783                                struct hrtimer_sleeper *timeout)
1784{
1785        /*
1786         * The task state is guaranteed to be set before another task can
1787         * wake it. set_current_state() is implemented using set_mb() and
1788         * queue_me() calls spin_unlock() upon completion, both serializing
1789         * access to the hash list and forcing another memory barrier.
1790         */
1791        set_current_state(TASK_INTERRUPTIBLE);
1792        queue_me(q, hb);
1793
1794        /* Arm the timer */
1795        if (timeout) {
1796                hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1797                if (!hrtimer_active(&timeout->timer))
1798                        timeout->task = NULL;
1799        }
1800
1801        /*
1802         * If we have been removed from the hash list, then another task
1803         * has tried to wake us, and we can skip the call to schedule().
1804         */
1805        if (likely(!plist_node_empty(&q->list))) {
1806                /*
1807                 * If the timer has already expired, current will already be
1808                 * flagged for rescheduling. Only call schedule if there
1809                 * is no timeout, or if it has yet to expire.
1810                 */
1811                if (!timeout || timeout->task)
1812                        freezable_schedule();
1813        }
1814        __set_current_state(TASK_RUNNING);
1815}
1816
1817/**
1818 * futex_wait_setup() - Prepare to wait on a futex
1819 * @uaddr:      the futex userspace address
1820 * @val:        the expected value
1821 * @flags:      futex flags (FLAGS_SHARED, etc.)
1822 * @q:          the associated futex_q
1823 * @hb:         storage for hash_bucket pointer to be returned to caller
1824 *
1825 * Setup the futex_q and locate the hash_bucket.  Get the futex value and
1826 * compare it with the expected value.  Handle atomic faults internally.
1827 * Return with the hb lock held and a q.key reference on success, and unlocked
1828 * with no q.key reference on failure.
1829 *
1830 * Return:
1831 *  0 - uaddr contains val and hb has been locked;
1832 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
1833 */
1834static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1835                           struct futex_q *q, struct futex_hash_bucket **hb)
1836{
1837        u32 uval;
1838        int ret;
1839
1840        /*
1841         * Access the page AFTER the hash-bucket is locked.
1842         * Order is important:
1843         *
1844         *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1845         *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
1846         *
1847         * The basic logical guarantee of a futex is that it blocks ONLY
1848         * if cond(var) is known to be true at the time of blocking, for
1849         * any cond.  If we locked the hash-bucket after testing *uaddr, that
1850         * would open a race condition where we could block indefinitely with
1851         * cond(var) false, which would violate the guarantee.
1852         *
1853         * On the other hand, we insert q and release the hash-bucket only
1854         * after testing *uaddr.  This guarantees that futex_wait() will NOT
1855         * absorb a wakeup if *uaddr does not match the desired values
1856         * while the syscall executes.
1857         */
1858retry:
1859        ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
1860        if (unlikely(ret != 0))
1861                return ret;
1862
1863retry_private:
1864        *hb = queue_lock(q);
1865
1866        ret = get_futex_value_locked(&uval, uaddr);
1867
1868        if (ret) {
1869                queue_unlock(q, *hb);
1870
1871                ret = get_user(uval, uaddr);
1872                if (ret)
1873                        goto out;
1874
1875                if (!(flags & FLAGS_SHARED))
1876                        goto retry_private;
1877
1878                put_futex_key(&q->key);
1879                goto retry;
1880        }
1881
1882        if (uval != val) {
1883                queue_unlock(q, *hb);
1884                ret = -EWOULDBLOCK;
1885        }
1886
1887out:
1888        if (ret)
1889                put_futex_key(&q->key);
1890        return ret;
1891}
1892
1893static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
1894                      ktime_t *abs_time, u32 bitset)
1895{
1896        struct hrtimer_sleeper timeout, *to = NULL;
1897        struct restart_block *restart;
1898        struct futex_hash_bucket *hb;
1899        struct futex_q q = futex_q_init;
1900        int ret;
1901
1902        if (!bitset)
1903                return -EINVAL;
1904        q.bitset = bitset;
1905
1906        if (abs_time) {
1907                to = &timeout;
1908
1909                hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
1910                                      CLOCK_REALTIME : CLOCK_MONOTONIC,
1911                                      HRTIMER_MODE_ABS);
1912                hrtimer_init_sleeper(to, current);
1913                hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1914                                             current->timer_slack_ns);
1915        }
1916
1917retry:
1918        /*
1919         * Prepare to wait on uaddr. On success, holds hb lock and increments
1920         * q.key refs.
1921         */
1922        ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
1923        if (ret)
1924                goto out;
1925
1926        /* queue_me and wait for wakeup, timeout, or a signal. */
1927        futex_wait_queue_me(hb, &q, to);
1928
1929        /* If we were woken (and unqueued), we succeeded, whatever. */
1930        ret = 0;
1931        /* unqueue_me() drops q.key ref */
1932        if (!unqueue_me(&q))
1933                goto out;
1934        ret = -ETIMEDOUT;
1935        if (to && !to->task)
1936                goto out;
1937
1938        /*
1939         * We expect signal_pending(current), but we might be the
1940         * victim of a spurious wakeup as well.
1941         */
1942        if (!signal_pending(current))
1943                goto retry;
1944
1945        ret = -ERESTARTSYS;
1946        if (!abs_time)
1947                goto out;
1948
1949        restart = &current_thread_info()->restart_block;
1950        restart->fn = futex_wait_restart;
1951        restart->futex.uaddr = uaddr;
1952        restart->futex.val = val;
1953        restart->futex.time = abs_time->tv64;
1954        restart->futex.bitset = bitset;
1955        restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
1956
1957        ret = -ERESTART_RESTARTBLOCK;
1958
1959out:
1960        if (to) {
1961                hrtimer_cancel(&to->timer);
1962                destroy_hrtimer_on_stack(&to->timer);
1963        }
1964        return ret;
1965}
1966
1967
1968static long futex_wait_restart(struct restart_block *restart)
1969{
1970        u32 __user *uaddr = restart->futex.uaddr;
1971        ktime_t t, *tp = NULL;
1972
1973        if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1974                t.tv64 = restart->futex.time;
1975                tp = &t;
1976        }
1977        restart->fn = do_no_restart_syscall;
1978
1979        return (long)futex_wait(uaddr, restart->futex.flags,
1980                                restart->futex.val, tp, restart->futex.bitset);
1981}
1982
1983
1984/*
1985 * Userspace tried a 0 -> TID atomic transition of the futex value
1986 * and failed. The kernel side here does the whole locking operation:
1987 * if there are waiters then it will block, it does PI, etc. (Due to
1988 * races the kernel might see a 0 value of the futex too.)
1989 */
1990static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
1991                         ktime_t *time, int trylock)
1992{
1993        struct hrtimer_sleeper timeout, *to = NULL;
1994        struct futex_hash_bucket *hb;
1995        struct futex_q q = futex_q_init;
1996        int res, ret;
1997
1998        if (refill_pi_state_cache())
1999                return -ENOMEM;
2000
2001        if (time) {
2002                to = &timeout;
2003                hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2004                                      HRTIMER_MODE_ABS);
2005                hrtimer_init_sleeper(to, current);
2006                hrtimer_set_expires(&to->timer, *time);
2007        }
2008
2009retry:
2010        ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2011        if (unlikely(ret != 0))
2012                goto out;
2013
2014retry_private:
2015        hb = queue_lock(&q);
2016
2017        ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2018        if (unlikely(ret)) {
2019                switch (ret) {
2020                case 1:
2021                        /* We got the lock. */
2022                        ret = 0;
2023                        goto out_unlock_put_key;
2024                case -EFAULT:
2025                        goto uaddr_faulted;
2026                case -EAGAIN:
2027                        /*
2028                         * Task is exiting and we just wait for the
2029                         * exit to complete.
2030                         */
2031                        queue_unlock(&q, hb);
2032                        put_futex_key(&q.key);
2033                        cond_resched();
2034                        goto retry;
2035                default:
2036                        goto out_unlock_put_key;
2037                }
2038        }
2039
2040        /*
2041         * Only actually queue now that the atomic ops are done:
2042         */
2043        queue_me(&q, hb);
2044
2045        WARN_ON(!q.pi_state);
2046        /*
2047         * Block on the PI mutex:
2048         */
2049        if (!trylock)
2050                ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2051        else {
2052                ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2053                /* Fixup the trylock return value: */
2054                ret = ret ? 0 : -EWOULDBLOCK;
2055        }
2056
2057        spin_lock(q.lock_ptr);
2058        /*
2059         * Fixup the pi_state owner and possibly acquire the lock if we
2060         * haven't already.
2061         */
2062        res = fixup_owner(uaddr, &q, !ret);
2063        /*
2064         * If fixup_owner() returned an error, proprogate that.  If it acquired
2065         * the lock, clear our -ETIMEDOUT or -EINTR.
2066         */
2067        if (res)
2068                ret = (res < 0) ? res : 0;
2069
2070        /*
2071         * If fixup_owner() faulted and was unable to handle the fault, unlock
2072         * it and return the fault to userspace.
2073         */
2074        if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2075                rt_mutex_unlock(&q.pi_state->pi_mutex);
2076
2077        /* Unqueue and drop the lock */
2078        unqueue_me_pi(&q);
2079
2080        goto out_put_key;
2081
2082out_unlock_put_key:
2083        queue_unlock(&q, hb);
2084
2085out_put_key:
2086        put_futex_key(&q.key);
2087out:
2088        if (to)
2089                destroy_hrtimer_on_stack(&to->timer);
2090        return ret != -EINTR ? ret : -ERESTARTNOINTR;
2091
2092uaddr_faulted:
2093        queue_unlock(&q, hb);
2094
2095        ret = fault_in_user_writeable(uaddr);
2096        if (ret)
2097                goto out_put_key;
2098
2099        if (!(flags & FLAGS_SHARED))
2100                goto retry_private;
2101
2102        put_futex_key(&q.key);
2103        goto retry;
2104}
2105
2106/*
2107 * Userspace attempted a TID -> 0 atomic transition, and failed.
2108 * This is the in-kernel slowpath: we look up the PI state (if any),
2109 * and do the rt-mutex unlock.
2110 */
2111static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2112{
2113        struct futex_hash_bucket *hb;
2114        struct futex_q *this, *next;
2115        struct plist_head *head;
2116        union futex_key key = FUTEX_KEY_INIT;
2117        u32 uval, vpid = task_pid_vnr(current);
2118        int ret;
2119
2120retry:
2121        if (get_user(uval, uaddr))
2122                return -EFAULT;
2123        /*
2124         * We release only a lock we actually own:
2125         */
2126        if ((uval & FUTEX_TID_MASK) != vpid)
2127                return -EPERM;
2128
2129        ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2130        if (unlikely(ret != 0))
2131                goto out;
2132
2133        hb = hash_futex(&key);
2134        spin_lock(&hb->lock);
2135
2136        /*
2137         * To avoid races, try to do the TID -> 0 atomic transition
2138         * again. If it succeeds then we can return without waking
2139         * anyone else up:
2140         */
2141        if (!(uval & FUTEX_OWNER_DIED) &&
2142            cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2143                goto pi_faulted;
2144        /*
2145         * Rare case: we managed to release the lock atomically,
2146         * no need to wake anyone else up:
2147         */
2148        if (unlikely(uval == vpid))
2149                goto out_unlock;
2150
2151        /*
2152         * Ok, other tasks may need to be woken up - check waiters
2153         * and do the wakeup if necessary:
2154         */
2155        head = &hb->chain;
2156
2157        plist_for_each_entry_safe(this, next, head, list) {
2158                if (!match_futex (&this->key, &key))
2159                        continue;
2160                ret = wake_futex_pi(uaddr, uval, this);
2161                /*
2162                 * The atomic access to the futex value
2163                 * generated a pagefault, so retry the
2164                 * user-access and the wakeup:
2165                 */
2166                if (ret == -EFAULT)
2167                        goto pi_faulted;
2168                goto out_unlock;
2169        }
2170        /*
2171         * No waiters - kernel unlocks the futex:
2172         */
2173        if (!(uval & FUTEX_OWNER_DIED)) {
2174                ret = unlock_futex_pi(uaddr, uval);
2175                if (ret == -EFAULT)
2176                        goto pi_faulted;
2177        }
2178
2179out_unlock:
2180        spin_unlock(&hb->lock);
2181        put_futex_key(&key);
2182
2183out:
2184        return ret;
2185
2186pi_faulted:
2187        spin_unlock(&hb->lock);
2188        put_futex_key(&key);
2189
2190        ret = fault_in_user_writeable(uaddr);
2191        if (!ret)
2192                goto retry;
2193
2194        return ret;
2195}
2196
2197/**
2198 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2199 * @hb:         the hash_bucket futex_q was original enqueued on
2200 * @q:          the futex_q woken while waiting to be requeued
2201 * @key2:       the futex_key of the requeue target futex
2202 * @timeout:    the timeout associated with the wait (NULL if none)
2203 *
2204 * Detect if the task was woken on the initial futex as opposed to the requeue
2205 * target futex.  If so, determine if it was a timeout or a signal that caused
2206 * the wakeup and return the appropriate error code to the caller.  Must be
2207 * called with the hb lock held.
2208 *
2209 * Return:
2210 *  0 = no early wakeup detected;
2211 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2212 */
2213static inline
2214int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2215                                   struct futex_q *q, union futex_key *key2,
2216                                   struct hrtimer_sleeper *timeout)
2217{
2218        int ret = 0;
2219
2220        /*
2221         * With the hb lock held, we avoid races while we process the wakeup.
2222         * We only need to hold hb (and not hb2) to ensure atomicity as the
2223         * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2224         * It can't be requeued from uaddr2 to something else since we don't
2225         * support a PI aware source futex for requeue.
2226         */
2227        if (!match_futex(&q->key, key2)) {
2228                WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2229                /*
2230                 * We were woken prior to requeue by a timeout or a signal.
2231                 * Unqueue the futex_q and determine which it was.
2232                 */
2233                plist_del(&q->list, &hb->chain);
2234
2235                /* Handle spurious wakeups gracefully */
2236                ret = -EWOULDBLOCK;
2237                if (timeout && !timeout->task)
2238                        ret = -ETIMEDOUT;
2239                else if (signal_pending(current))
2240                        ret = -ERESTARTNOINTR;
2241        }
2242        return ret;
2243}
2244
2245/**
2246 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2247 * @uaddr:      the futex we initially wait on (non-pi)
2248 * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2249 *              the same type, no requeueing from private to shared, etc.
2250 * @val:        the expected value of uaddr
2251 * @abs_time:   absolute timeout
2252 * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
2253 * @uaddr2:     the pi futex we will take prior to returning to user-space
2254 *
2255 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2256 * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
2257 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2258 * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
2259 * without one, the pi logic would not know which task to boost/deboost, if
2260 * there was a need to.
2261 *
2262 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2263 * via the following--
2264 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2265 * 2) wakeup on uaddr2 after a requeue
2266 * 3) signal
2267 * 4) timeout
2268 *
2269 * If 3, cleanup and return -ERESTARTNOINTR.
2270 *
2271 * If 2, we may then block on trying to take the rt_mutex and return via:
2272 * 5) successful lock
2273 * 6) signal
2274 * 7) timeout
2275 * 8) other lock acquisition failure
2276 *
2277 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2278 *
2279 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2280 *
2281 * Return:
2282 *  0 - On success;
2283 * <0 - On error
2284 */
2285static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2286                                 u32 val, ktime_t *abs_time, u32 bitset,
2287                                 u32 __user *uaddr2)
2288{
2289        struct hrtimer_sleeper timeout, *to = NULL;
2290        struct rt_mutex_waiter rt_waiter;
2291        struct rt_mutex *pi_mutex = NULL;
2292        struct futex_hash_bucket *hb;
2293        union futex_key key2 = FUTEX_KEY_INIT;
2294        struct futex_q q = futex_q_init;
2295        int res, ret;
2296
2297        if (uaddr == uaddr2)
2298                return -EINVAL;
2299
2300        if (!bitset)
2301                return -EINVAL;
2302
2303        if (abs_time) {
2304                to = &timeout;
2305                hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2306                                      CLOCK_REALTIME : CLOCK_MONOTONIC,
2307                                      HRTIMER_MODE_ABS);
2308                hrtimer_init_sleeper(to, current);
2309                hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2310                                             current->timer_slack_ns);
2311        }
2312
2313        /*
2314         * The waiter is allocated on our stack, manipulated by the requeue
2315         * code while we sleep on uaddr.
2316         */
2317        debug_rt_mutex_init_waiter(&rt_waiter);
2318        rt_waiter.task = NULL;
2319
2320        ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2321        if (unlikely(ret != 0))
2322                goto out;
2323
2324        q.bitset = bitset;
2325        q.rt_waiter = &rt_waiter;
2326        q.requeue_pi_key = &key2;
2327
2328        /*
2329         * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2330         * count.
2331         */
2332        ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2333        if (ret)
2334                goto out_key2;
2335
2336        /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2337        futex_wait_queue_me(hb, &q, to);
2338
2339        spin_lock(&hb->lock);
2340        ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2341        spin_unlock(&hb->lock);
2342        if (ret)
2343                goto out_put_keys;
2344
2345        /*
2346         * In order for us to be here, we know our q.key == key2, and since
2347         * we took the hb->lock above, we also know that futex_requeue() has
2348         * completed and we no longer have to concern ourselves with a wakeup
2349         * race with the atomic proxy lock acquisition by the requeue code. The
2350         * futex_requeue dropped our key1 reference and incremented our key2
2351         * reference count.
2352         */
2353
2354        /* Check if the requeue code acquired the second futex for us. */
2355        if (!q.rt_waiter) {
2356                /*
2357                 * Got the lock. We might not be the anticipated owner if we
2358                 * did a lock-steal - fix up the PI-state in that case.
2359                 */
2360                if (q.pi_state && (q.pi_state->owner != current)) {
2361                        spin_lock(q.lock_ptr);
2362                        ret = fixup_pi_state_owner(uaddr2, &q, current);
2363                        spin_unlock(q.lock_ptr);
2364                }
2365        } else {
2366                /*
2367                 * We have been woken up by futex_unlock_pi(), a timeout, or a
2368                 * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
2369                 * the pi_state.
2370                 */
2371                WARN_ON(!q.pi_state);
2372                pi_mutex = &q.pi_state->pi_mutex;
2373                ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2374                debug_rt_mutex_free_waiter(&rt_waiter);
2375
2376                spin_lock(q.lock_ptr);
2377                /*
2378                 * Fixup the pi_state owner and possibly acquire the lock if we
2379                 * haven't already.
2380                 */
2381                res = fixup_owner(uaddr2, &q, !ret);
2382                /*
2383                 * If fixup_owner() returned an error, proprogate that.  If it
2384                 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2385                 */
2386                if (res)
2387                        ret = (res < 0) ? res : 0;
2388
2389                /* Unqueue and drop the lock. */
2390                unqueue_me_pi(&q);
2391        }
2392
2393        /*
2394         * If fixup_pi_state_owner() faulted and was unable to handle the
2395         * fault, unlock the rt_mutex and return the fault to userspace.
2396         */
2397        if (ret == -EFAULT) {
2398                if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2399                        rt_mutex_unlock(pi_mutex);
2400        } else if (ret == -EINTR) {
2401                /*
2402                 * We've already been requeued, but cannot restart by calling
2403                 * futex_lock_pi() directly. We could restart this syscall, but
2404                 * it would detect that the user space "val" changed and return
2405                 * -EWOULDBLOCK.  Save the overhead of the restart and return
2406                 * -EWOULDBLOCK directly.
2407                 */
2408                ret = -EWOULDBLOCK;
2409        }
2410
2411out_put_keys:
2412        put_futex_key(&q.key);
2413out_key2:
2414        put_futex_key(&key2);
2415
2416out:
2417        if (to) {
2418                hrtimer_cancel(&to->timer);
2419                destroy_hrtimer_on_stack(&to->timer);
2420        }
2421        return ret;
2422}
2423
2424/*
2425 * Support for robust futexes: the kernel cleans up held futexes at
2426 * thread exit time.
2427 *
2428 * Implementation: user-space maintains a per-thread list of locks it
2429 * is holding. Upon do_exit(), the kernel carefully walks this list,
2430 * and marks all locks that are owned by this thread with the
2431 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2432 * always manipulated with the lock held, so the list is private and
2433 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2434 * field, to allow the kernel to clean up if the thread dies after
2435 * acquiring the lock, but just before it could have added itself to
2436 * the list. There can only be one such pending lock.
2437 */
2438
2439/**
2440 * sys_set_robust_list() - Set the robust-futex list head of a task
2441 * @head:       pointer to the list-head
2442 * @len:        length of the list-head, as userspace expects
2443 */
2444SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2445                size_t, len)
2446{
2447        if (!futex_cmpxchg_enabled)
2448                return -ENOSYS;
2449        /*
2450         * The kernel knows only one size for now:
2451         */
2452        if (unlikely(len != sizeof(*head)))
2453                return -EINVAL;
2454
2455        current->robust_list = head;
2456
2457        return 0;
2458}
2459
2460/**
2461 * sys_get_robust_list() - Get the robust-futex list head of a task
2462 * @pid:        pid of the process [zero for current task]
2463 * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
2464 * @len_ptr:    pointer to a length field, the kernel fills in the header size
2465 */
2466SYSCALL_DEFINE3(get_robust_list, int, pid,
2467                struct robust_list_head __user * __user *, head_ptr,
2468                size_t __user *, len_ptr)
2469{
2470        struct robust_list_head __user *head;
2471        unsigned long ret;
2472        struct task_struct *p;
2473
2474        if (!futex_cmpxchg_enabled)
2475                return -ENOSYS;
2476
2477        rcu_read_lock();
2478
2479        ret = -ESRCH;
2480        if (!pid)
2481                p = current;
2482        else {
2483                p = find_task_by_vpid(pid);
2484                if (!p)
2485                        goto err_unlock;
2486        }
2487
2488        ret = -EPERM;
2489        if (!ptrace_may_access(p, PTRACE_MODE_READ))
2490                goto err_unlock;
2491
2492        head = p->robust_list;
2493        rcu_read_unlock();
2494
2495        if (put_user(sizeof(*head), len_ptr))
2496                return -EFAULT;
2497        return put_user(head, head_ptr);
2498
2499err_unlock:
2500        rcu_read_unlock();
2501
2502        return ret;
2503}
2504
2505/*
2506 * Process a futex-list entry, check whether it's owned by the
2507 * dying task, and do notification if so:
2508 */
2509int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2510{
2511        u32 uval, uninitialized_var(nval), mval;
2512
2513retry:
2514        if (get_user(uval, uaddr))
2515                return -1;
2516
2517        if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2518                /*
2519                 * Ok, this dying thread is truly holding a futex
2520                 * of interest. Set the OWNER_DIED bit atomically
2521                 * via cmpxchg, and if the value had FUTEX_WAITERS
2522                 * set, wake up a waiter (if any). (We have to do a
2523                 * futex_wake() even if OWNER_DIED is already set -
2524                 * to handle the rare but possible case of recursive
2525                 * thread-death.) The rest of the cleanup is done in
2526                 * userspace.
2527                 */
2528                mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2529                /*
2530                 * We are not holding a lock here, but we want to have
2531                 * the pagefault_disable/enable() protection because
2532                 * we want to handle the fault gracefully. If the
2533                 * access fails we try to fault in the futex with R/W
2534                 * verification via get_user_pages. get_user() above
2535                 * does not guarantee R/W access. If that fails we
2536                 * give up and leave the futex locked.
2537                 */
2538                if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2539                        if (fault_in_user_writeable(uaddr))
2540                                return -1;
2541                        goto retry;
2542                }
2543                if (nval != uval)
2544                        goto retry;
2545
2546                /*
2547                 * Wake robust non-PI futexes here. The wakeup of
2548                 * PI futexes happens in exit_pi_state():
2549                 */
2550                if (!pi && (uval & FUTEX_WAITERS))
2551                        futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2552        }
2553        return 0;
2554}
2555
2556/*
2557 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2558 */
2559static inline int fetch_robust_entry(struct robust_list __user **entry,
2560                                     struct robust_list __user * __user *head,
2561                                     unsigned int *pi)
2562{
2563        unsigned long uentry;
2564
2565        if (get_user(uentry, (unsigned long __user *)head))
2566                return -EFAULT;
2567
2568        *entry = (void __user *)(uentry & ~1UL);
2569        *pi = uentry & 1;
2570
2571        return 0;
2572}
2573
2574/*
2575 * Walk curr->robust_list (very carefully, it's a userspace list!)
2576 * and mark any locks found there dead, and notify any waiters.
2577 *
2578 * We silently return on any sign of list-walking problem.
2579 */
2580void exit_robust_list(struct task_struct *curr)
2581{
2582        struct robust_list_head __user *head = curr->robust_list;
2583        struct robust_list __user *entry, *next_entry, *pending;
2584        unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2585        unsigned int uninitialized_var(next_pi);
2586        unsigned long futex_offset;
2587        int rc;
2588
2589        if (!futex_cmpxchg_enabled)
2590                return;
2591
2592        /*
2593         * Fetch the list head (which was registered earlier, via
2594         * sys_set_robust_list()):
2595         */
2596        if (fetch_robust_entry(&entry, &head->list.next, &pi))
2597                return;
2598        /*
2599         * Fetch the relative futex offset:
2600         */
2601        if (get_user(futex_offset, &head->futex_offset))
2602                return;
2603        /*
2604         * Fetch any possibly pending lock-add first, and handle it
2605         * if it exists:
2606         */
2607        if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2608                return;
2609
2610        next_entry = NULL;      /* avoid warning with gcc */
2611        while (entry != &head->list) {
2612                /*
2613                 * Fetch the next entry in the list before calling
2614                 * handle_futex_death:
2615                 */
2616                rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2617                /*
2618                 * A pending lock might already be on the list, so
2619                 * don't process it twice:
2620                 */
2621                if (entry != pending)
2622                        if (handle_futex_death((void __user *)entry + futex_offset,
2623                                                curr, pi))
2624                                return;
2625                if (rc)
2626                        return;
2627                entry = next_entry;
2628                pi = next_pi;
2629                /*
2630                 * Avoid excessively long or circular lists:
2631                 */
2632                if (!--limit)
2633                        break;
2634
2635                cond_resched();
2636        }
2637
2638        if (pending)
2639                handle_futex_death((void __user *)pending + futex_offset,
2640                                   curr, pip);
2641}
2642
2643long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2644                u32 __user *uaddr2, u32 val2, u32 val3)
2645{
2646        int cmd = op & FUTEX_CMD_MASK;
2647        unsigned int flags = 0;
2648
2649        if (!(op & FUTEX_PRIVATE_FLAG))
2650                flags |= FLAGS_SHARED;
2651
2652        if (op & FUTEX_CLOCK_REALTIME) {
2653                flags |= FLAGS_CLOCKRT;
2654                if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2655                        return -ENOSYS;
2656        }
2657
2658        switch (cmd) {
2659        case FUTEX_LOCK_PI:
2660        case FUTEX_UNLOCK_PI:
2661        case FUTEX_TRYLOCK_PI:
2662        case FUTEX_WAIT_REQUEUE_PI:
2663        case FUTEX_CMP_REQUEUE_PI:
2664                if (!futex_cmpxchg_enabled)
2665                        return -ENOSYS;
2666        }
2667
2668        switch (cmd) {
2669        case FUTEX_WAIT:
2670                val3 = FUTEX_BITSET_MATCH_ANY;
2671        case FUTEX_WAIT_BITSET:
2672                return futex_wait(uaddr, flags, val, timeout, val3);
2673        case FUTEX_WAKE:
2674                val3 = FUTEX_BITSET_MATCH_ANY;
2675        case FUTEX_WAKE_BITSET:
2676                return futex_wake(uaddr, flags, val, val3);
2677        case FUTEX_REQUEUE:
2678                return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2679        case FUTEX_CMP_REQUEUE:
2680                return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2681        case FUTEX_WAKE_OP:
2682                return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2683        case FUTEX_LOCK_PI:
2684                return futex_lock_pi(uaddr, flags, val, timeout, 0);
2685        case FUTEX_UNLOCK_PI:
2686                return futex_unlock_pi(uaddr, flags);
2687        case FUTEX_TRYLOCK_PI:
2688                return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2689        case FUTEX_WAIT_REQUEUE_PI:
2690                val3 = FUTEX_BITSET_MATCH_ANY;
2691                return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2692                                             uaddr2);
2693        case FUTEX_CMP_REQUEUE_PI:
2694                return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2695        }
2696        return -ENOSYS;
2697}
2698
2699
2700SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2701                struct timespec __user *, utime, u32 __user *, uaddr2,
2702                u32, val3)
2703{
2704        struct timespec ts;
2705        ktime_t t, *tp = NULL;
2706        u32 val2 = 0;
2707        int cmd = op & FUTEX_CMD_MASK;
2708
2709        if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2710                      cmd == FUTEX_WAIT_BITSET ||
2711                      cmd == FUTEX_WAIT_REQUEUE_PI)) {
2712                if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2713                        return -EFAULT;
2714                if (!timespec_valid(&ts))
2715                        return -EINVAL;
2716
2717                t = timespec_to_ktime(ts);
2718                if (cmd == FUTEX_WAIT)
2719                        t = ktime_add_safe(ktime_get(), t);
2720                tp = &t;
2721        }
2722        /*
2723         * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2724         * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2725         */
2726        if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2727            cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2728                val2 = (u32) (unsigned long) utime;
2729
2730        return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2731}
2732
2733static int __init futex_init(void)
2734{
2735        u32 curval;
2736        int i;
2737
2738        /*
2739         * This will fail and we want it. Some arch implementations do
2740         * runtime detection of the futex_atomic_cmpxchg_inatomic()
2741         * functionality. We want to know that before we call in any
2742         * of the complex code paths. Also we want to prevent
2743         * registration of robust lists in that case. NULL is
2744         * guaranteed to fault and we get -EFAULT on functional
2745         * implementation, the non-functional ones will return
2746         * -ENOSYS.
2747         */
2748        if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2749                futex_cmpxchg_enabled = 1;
2750
2751        for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2752                plist_head_init(&futex_queues[i].chain);
2753                spin_lock_init(&futex_queues[i].lock);
2754        }
2755
2756        return 0;
2757}
2758__initcall(futex_init);
2759
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