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-rw-r--r--kernel/futex.c33
1 files changed, 14 insertions, 19 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 438701adce23..e6a4d72bca3d 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -114,7 +114,9 @@ struct futex_q {
114}; 114};
115 115
116/* 116/*
117 * Split the global futex_lock into every hash list lock. 117 * Hash buckets are shared by all the futex_keys that hash to the same
118 * location. Each key may have multiple futex_q structures, one for each task
119 * waiting on a futex.
118 */ 120 */
119struct futex_hash_bucket { 121struct futex_hash_bucket {
120 spinlock_t lock; 122 spinlock_t lock;
@@ -189,8 +191,7 @@ static void drop_futex_key_refs(union futex_key *key)
189/** 191/**
190 * get_futex_key - Get parameters which are the keys for a futex. 192 * get_futex_key - Get parameters which are the keys for a futex.
191 * @uaddr: virtual address of the futex 193 * @uaddr: virtual address of the futex
192 * @shared: NULL for a PROCESS_PRIVATE futex, 194 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
193 * &current->mm->mmap_sem for a PROCESS_SHARED futex
194 * @key: address where result is stored. 195 * @key: address where result is stored.
195 * 196 *
196 * Returns a negative error code or 0 197 * Returns a negative error code or 0
@@ -200,9 +201,7 @@ static void drop_futex_key_refs(union futex_key *key)
200 * offset_within_page). For private mappings, it's (uaddr, current->mm). 201 * offset_within_page). For private mappings, it's (uaddr, current->mm).
201 * We can usually work out the index without swapping in the page. 202 * We can usually work out the index without swapping in the page.
202 * 203 *
203 * fshared is NULL for PROCESS_PRIVATE futexes 204 * lock_page() might sleep, the caller should not hold a spinlock.
204 * For other futexes, it points to &current->mm->mmap_sem and
205 * caller must have taken the reader lock. but NOT any spinlocks.
206 */ 205 */
207static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key) 206static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
208{ 207{
@@ -589,10 +588,9 @@ static void wake_futex(struct futex_q *q)
589 * The waiting task can free the futex_q as soon as this is written, 588 * The waiting task can free the futex_q as soon as this is written,
590 * without taking any locks. This must come last. 589 * without taking any locks. This must come last.
591 * 590 *
592 * A memory barrier is required here to prevent the following store 591 * A memory barrier is required here to prevent the following store to
593 * to lock_ptr from getting ahead of the wakeup. Clearing the lock 592 * lock_ptr from getting ahead of the wakeup. Clearing the lock at the
594 * at the end of wake_up_all() does not prevent this store from 593 * end of wake_up() does not prevent this store from moving.
595 * moving.
596 */ 594 */
597 smp_wmb(); 595 smp_wmb();
598 q->lock_ptr = NULL; 596 q->lock_ptr = NULL;
@@ -693,8 +691,7 @@ double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
693} 691}
694 692
695/* 693/*
696 * Wake up all waiters hashed on the physical page that is mapped 694 * Wake up waiters matching bitset queued on this futex (uaddr).
697 * to this virtual address:
698 */ 695 */
699static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset) 696static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
700{ 697{
@@ -1076,11 +1073,9 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1076 * in the user space variable. This must be atomic as we have 1073 * in the user space variable. This must be atomic as we have
1077 * to preserve the owner died bit here. 1074 * to preserve the owner died bit here.
1078 * 1075 *
1079 * Note: We write the user space value _before_ changing the 1076 * Note: We write the user space value _before_ changing the pi_state
1080 * pi_state because we can fault here. Imagine swapped out 1077 * because we can fault here. Imagine swapped out pages or a fork
1081 * pages or a fork, which was running right before we acquired 1078 * that marked all the anonymous memory readonly for cow.
1082 * mmap_sem, that marked all the anonymous memory readonly for
1083 * cow.
1084 * 1079 *
1085 * Modifying pi_state _before_ the user space value would 1080 * Modifying pi_state _before_ the user space value would
1086 * leave the pi_state in an inconsistent state when we fault 1081 * leave the pi_state in an inconsistent state when we fault
@@ -1188,7 +1183,7 @@ retry:
1188 hb = queue_lock(&q); 1183 hb = queue_lock(&q);
1189 1184
1190 /* 1185 /*
1191 * Access the page AFTER the futex is queued. 1186 * Access the page AFTER the hash-bucket is locked.
1192 * Order is important: 1187 * Order is important:
1193 * 1188 *
1194 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); 1189 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
@@ -1204,7 +1199,7 @@ retry:
1204 * a wakeup when *uaddr != val on entry to the syscall. This is 1199 * a wakeup when *uaddr != val on entry to the syscall. This is
1205 * rare, but normal. 1200 * rare, but normal.
1206 * 1201 *
1207 * for shared futexes, we hold the mmap semaphore, so the mapping 1202 * For shared futexes, we hold the mmap semaphore, so the mapping
1208 * cannot have changed since we looked it up in get_futex_key. 1203 * cannot have changed since we looked it up in get_futex_key.
1209 */ 1204 */
1210 ret = get_futex_value_locked(&uval, uaddr); 1205 ret = get_futex_value_locked(&uval, uaddr);