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