diff options
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 33 |
1 files changed, 14 insertions, 19 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 438701adce2..e6a4d72bca3 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -114,7 +114,9 @@ struct futex_q { }; /* - * Split the global futex_lock into every hash list lock. + * Hash buckets are shared by all the futex_keys that hash to the same + * location. Each key may have multiple futex_q structures, one for each task + * waiting on a futex. */ struct futex_hash_bucket { spinlock_t lock; @@ -189,8 +191,7 @@ static void drop_futex_key_refs(union futex_key *key) /** * get_futex_key - Get parameters which are the keys for a futex. * @uaddr: virtual address of the futex - * @shared: NULL for a PROCESS_PRIVATE futex, - * ¤t->mm->mmap_sem for a PROCESS_SHARED futex + * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED * @key: address where result is stored. * * Returns a negative error code or 0 @@ -200,9 +201,7 @@ static void drop_futex_key_refs(union futex_key *key) * offset_within_page). For private mappings, it's (uaddr, current->mm). * We can usually work out the index without swapping in the page. * - * fshared is NULL for PROCESS_PRIVATE futexes - * For other futexes, it points to ¤t->mm->mmap_sem and - * caller must have taken the reader lock. but NOT any spinlocks. + * lock_page() might sleep, the caller should not hold a spinlock. */ static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key) { @@ -589,10 +588,9 @@ static void wake_futex(struct futex_q *q) * The waiting task can free the futex_q as soon as this is written, * without taking any locks. This must come last. * - * A memory barrier is required here to prevent the following store - * to lock_ptr from getting ahead of the wakeup. Clearing the lock - * at the end of wake_up_all() does not prevent this store from - * moving. + * A memory barrier is required here to prevent the following store to + * lock_ptr from getting ahead of the wakeup. Clearing the lock at the + * end of wake_up() does not prevent this store from moving. */ smp_wmb(); q->lock_ptr = NULL; @@ -693,8 +691,7 @@ double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) } /* - * Wake up all waiters hashed on the physical page that is mapped - * to this virtual address: + * Wake up waiters matching bitset queued on this futex (uaddr). */ static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset) { @@ -1076,11 +1073,9 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, * in the user space variable. This must be atomic as we have * to preserve the owner died bit here. * - * Note: We write the user space value _before_ changing the - * pi_state because we can fault here. Imagine swapped out - * pages or a fork, which was running right before we acquired - * mmap_sem, that marked all the anonymous memory readonly for - * cow. + * Note: We write the user space value _before_ changing the pi_state + * because we can fault here. Imagine swapped out pages or a fork + * that marked all the anonymous memory readonly for cow. * * Modifying pi_state _before_ the user space value would * leave the pi_state in an inconsistent state when we fault @@ -1188,7 +1183,7 @@ retry: hb = queue_lock(&q); /* - * Access the page AFTER the futex is queued. + * Access the page AFTER the hash-bucket is locked. * Order is important: * * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); @@ -1204,7 +1199,7 @@ retry: * a wakeup when *uaddr != val on entry to the syscall. This is * rare, but normal. * - * for shared futexes, we hold the mmap semaphore, so the mapping + * For shared futexes, we hold the mmap semaphore, so the mapping * cannot have changed since we looked it up in get_futex_key. */ ret = get_futex_value_locked(&uval, uaddr); |