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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 {
};
/*
- * 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,
- * &current->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 &current->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);