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Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: futex: Add memory barrier commentary to futex_wait_queue_me() futex: Fix wakeup race by setting TASK_INTERRUPTIBLE before queue_me() futex: Correct futex_q woken state commentary futex: Make function kernel-doc commentary consistent futex: Correct queue_me and unqueue_me commentary futex: Correct futex_wait_requeue_pi() commentary
This commit is contained in:
Linus Torvalds
commit
3b383767c4
137
kernel/futex.c
137
kernel/futex.c
@ -89,36 +89,36 @@ struct futex_pi_state {
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union futex_key key;
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};
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/*
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* We use this hashed waitqueue instead of a normal wait_queue_t, so
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/**
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* struct futex_q - The hashed futex queue entry, one per waiting task
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* @task: the task waiting on the futex
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* @lock_ptr: the hash bucket lock
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* @key: the key the futex is hashed on
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* @pi_state: optional priority inheritance state
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* @rt_waiter: rt_waiter storage for use with requeue_pi
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* @requeue_pi_key: the requeue_pi target futex key
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* @bitset: bitset for the optional bitmasked wakeup
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*
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* We use this hashed waitqueue, instead of a normal wait_queue_t, so
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* we can wake only the relevant ones (hashed queues may be shared).
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*
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* A futex_q has a woken state, just like tasks have TASK_RUNNING.
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* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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* The order of wakup is always to make the first condition true, then
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* wake up q->waiter, then make the second condition true.
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* the second.
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*
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* PI futexes are typically woken before they are removed from the hash list via
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* the rt_mutex code. See unqueue_me_pi().
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*/
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struct futex_q {
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struct plist_node list;
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/* Waiter reference */
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struct task_struct *task;
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/* Which hash list lock to use: */
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spinlock_t *lock_ptr;
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/* Key which the futex is hashed on: */
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union futex_key key;
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/* Optional priority inheritance state: */
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struct futex_pi_state *pi_state;
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/* rt_waiter storage for requeue_pi: */
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struct rt_mutex_waiter *rt_waiter;
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/* The expected requeue pi target futex key: */
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union futex_key *requeue_pi_key;
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/* Bitset for the optional bitmasked wakeup */
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u32 bitset;
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};
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@ -198,11 +198,12 @@ static void drop_futex_key_refs(union futex_key *key)
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}
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/**
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* get_futex_key - Get parameters which are the keys for a futex.
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* @uaddr: virtual address of the futex
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* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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* @key: address where result is stored.
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* @rw: mapping needs to be read/write (values: VERIFY_READ, VERIFY_WRITE)
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* get_futex_key() - Get parameters which are the keys for a futex
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* @uaddr: virtual address of the futex
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* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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* @key: address where result is stored.
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* @rw: mapping needs to be read/write (values: VERIFY_READ,
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* VERIFY_WRITE)
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*
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* Returns a negative error code or 0
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* The key words are stored in *key on success.
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@ -288,8 +289,8 @@ void put_futex_key(int fshared, union futex_key *key)
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drop_futex_key_refs(key);
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}
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/*
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* fault_in_user_writeable - fault in user address and verify RW access
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/**
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* fault_in_user_writeable() - Fault in user address and verify RW access
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* @uaddr: pointer to faulting user space address
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*
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* Slow path to fixup the fault we just took in the atomic write
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@ -309,8 +310,8 @@ static int fault_in_user_writeable(u32 __user *uaddr)
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/**
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* futex_top_waiter() - Return the highest priority waiter on a futex
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* @hb: the hash bucket the futex_q's reside in
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* @key: the futex key (to distinguish it from other futex futex_q's)
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* @hb: the hash bucket the futex_q's reside in
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* @key: the futex key (to distinguish it from other futex futex_q's)
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*
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* Must be called with the hb lock held.
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*/
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@ -588,7 +589,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
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}
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/**
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* futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
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* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
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* @uaddr: the pi futex user address
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* @hb: the pi futex hash bucket
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* @key: the futex key associated with uaddr and hb
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@ -1011,9 +1012,9 @@ void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
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/**
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* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
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* q: the futex_q
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* key: the key of the requeue target futex
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* hb: the hash_bucket of the requeue target futex
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* @q: the futex_q
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* @key: the key of the requeue target futex
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* @hb: the hash_bucket of the requeue target futex
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*
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* During futex_requeue, with requeue_pi=1, it is possible to acquire the
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* target futex if it is uncontended or via a lock steal. Set the futex_q key
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@ -1350,6 +1351,25 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
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return hb;
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}
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static inline void
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queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
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{
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spin_unlock(&hb->lock);
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drop_futex_key_refs(&q->key);
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}
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/**
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* queue_me() - Enqueue the futex_q on the futex_hash_bucket
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* @q: The futex_q to enqueue
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* @hb: The destination hash bucket
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*
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* The hb->lock must be held by the caller, and is released here. A call to
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* queue_me() is typically paired with exactly one call to unqueue_me(). The
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* exceptions involve the PI related operations, which may use unqueue_me_pi()
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* or nothing if the unqueue is done as part of the wake process and the unqueue
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* state is implicit in the state of woken task (see futex_wait_requeue_pi() for
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* an example).
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*/
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static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
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{
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int prio;
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@ -1373,19 +1393,17 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
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spin_unlock(&hb->lock);
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}
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static inline void
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queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
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{
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spin_unlock(&hb->lock);
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drop_futex_key_refs(&q->key);
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}
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/*
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* queue_me and unqueue_me must be called as a pair, each
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* exactly once. They are called with the hashed spinlock held.
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/**
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* unqueue_me() - Remove the futex_q from its futex_hash_bucket
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* @q: The futex_q to unqueue
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*
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* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
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* be paired with exactly one earlier call to queue_me().
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*
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* Returns:
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* 1 - if the futex_q was still queued (and we removed unqueued it)
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* 0 - if the futex_q was already removed by the waking thread
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*/
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/* Return 1 if we were still queued (ie. 0 means we were woken) */
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static int unqueue_me(struct futex_q *q)
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{
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spinlock_t *lock_ptr;
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@ -1638,17 +1656,14 @@ out:
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static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
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struct hrtimer_sleeper *timeout)
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{
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queue_me(q, hb);
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/*
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* There might have been scheduling since the queue_me(), as we
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* cannot hold a spinlock across the get_user() in case it
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* faults, and we cannot just set TASK_INTERRUPTIBLE state when
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* queueing ourselves into the futex hash. This code thus has to
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* rely on the futex_wake() code removing us from hash when it
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* wakes us up.
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* The task state is guaranteed to be set before another task can
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* wake it. set_current_state() is implemented using set_mb() and
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* queue_me() calls spin_unlock() upon completion, both serializing
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* access to the hash list and forcing another memory barrier.
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*/
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set_current_state(TASK_INTERRUPTIBLE);
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queue_me(q, hb);
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/* Arm the timer */
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if (timeout) {
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@ -1658,8 +1673,8 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
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}
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/*
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* !plist_node_empty() is safe here without any lock.
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* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
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* If we have been removed from the hash list, then another task
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* has tried to wake us, and we can skip the call to schedule().
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*/
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if (likely(!plist_node_empty(&q->list))) {
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/*
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@ -2114,12 +2129,12 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
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/**
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* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
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* @uaddr: the futex we initialyl wait on (non-pi)
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* @uaddr: the futex we initially wait on (non-pi)
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* @fshared: whether the futexes are shared (1) or not (0). They must be
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* the same type, no requeueing from private to shared, etc.
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* @val: the expected value of uaddr
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* @abs_time: absolute timeout
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* @bitset: 32 bit wakeup bitset set by userspace, defaults to all.
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* @bitset: 32 bit wakeup bitset set by userspace, defaults to all
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* @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
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* @uaddr2: the pi futex we will take prior to returning to user-space
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*
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@ -2246,7 +2261,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
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res = fixup_owner(uaddr2, fshared, &q, !ret);
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/*
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* If fixup_owner() returned an error, proprogate that. If it
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* acquired the lock, clear our -ETIMEDOUT or -EINTR.
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* acquired the lock, clear -ETIMEDOUT or -EINTR.
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*/
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if (res)
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ret = (res < 0) ? res : 0;
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@ -2302,9 +2317,9 @@ out:
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*/
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/**
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* sys_set_robust_list - set the robust-futex list head of a task
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* @head: pointer to the list-head
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* @len: length of the list-head, as userspace expects
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* sys_set_robust_list() - Set the robust-futex list head of a task
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* @head: pointer to the list-head
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* @len: length of the list-head, as userspace expects
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*/
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SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
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size_t, len)
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@ -2323,10 +2338,10 @@ SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
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}
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/**
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* sys_get_robust_list - get the robust-futex list head of a task
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* @pid: pid of the process [zero for current task]
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* @head_ptr: pointer to a list-head pointer, the kernel fills it in
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* @len_ptr: pointer to a length field, the kernel fills in the header size
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* sys_get_robust_list() - Get the robust-futex list head of a task
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* @pid: pid of the process [zero for current task]
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* @head_ptr: pointer to a list-head pointer, the kernel fills it in
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* @len_ptr: pointer to a length field, the kernel fills in the header size
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*/
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SYSCALL_DEFINE3(get_robust_list, int, pid,
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struct robust_list_head __user * __user *, head_ptr,
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