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