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