X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=kernel%2Ffutex.c;h=fb65e822fc41ae698c282aeadc6933b411aa8a78;hb=82ead7fe41da960ed80652d13d5a1072f85f5aca;hp=6c498b145a4f325da3731802381586b44b2ce7f7;hpb=56ec1607b15b6a5f6de5aab14f16a763b88296fc;p=safe%2Fjmp%2Flinux-2.6

diff --git a/kernel/futex.c b/kernel/futex.c
index 6c498b1..fb65e82 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -89,36 +89,36 @@ struct futex_pi_state {
 	union futex_key key;
 };
 
-/*
- * We use this hashed waitqueue instead of a normal wait_queue_t, so
+/**
+ * struct futex_q - The hashed futex queue entry, one per waiting task
+ * @task:		the task waiting on the futex
+ * @lock_ptr:		the hash bucket lock
+ * @key:		the key the futex is hashed on
+ * @pi_state:		optional priority inheritance state
+ * @rt_waiter:		rt_waiter storage for use with requeue_pi
+ * @requeue_pi_key:	the requeue_pi target futex key
+ * @bitset:		bitset for the optional bitmasked wakeup
+ *
+ * We use this hashed waitqueue, instead of a normal wait_queue_t, so
  * we can wake only the relevant ones (hashed queues may be shared).
  *
  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
  * The order of wakup is always to make the first condition true, then
- * wake up q->waiter, then make the second condition true.
+ * the second.
+ *
+ * PI futexes are typically woken before they are removed from the hash list via
+ * the rt_mutex code. See unqueue_me_pi().
  */
 struct futex_q {
 	struct plist_node list;
-	/* Waiter reference */
-	struct task_struct *task;
 
-	/* Which hash list lock to use: */
+	struct task_struct *task;
 	spinlock_t *lock_ptr;
-
-	/* Key which the futex is hashed on: */
 	union futex_key key;
-
-	/* Optional priority inheritance state: */
 	struct futex_pi_state *pi_state;
-
-	/* rt_waiter storage for requeue_pi: */
 	struct rt_mutex_waiter *rt_waiter;
-
-	/* The expected requeue pi target futex key: */
 	union futex_key *requeue_pi_key;
-
-	/* Bitset for the optional bitmasked wakeup */
 	u32 bitset;
 };
 
@@ -150,7 +150,8 @@ static struct futex_hash_bucket *hash_futex(union futex_key *key)
  */
 static inline int match_futex(union futex_key *key1, union futex_key *key2)
 {
-	return (key1->both.word == key2->both.word
+	return (key1 && key2
+		&& key1->both.word == key2->both.word
 		&& key1->both.ptr == key2->both.ptr
 		&& key1->both.offset == key2->both.offset);
 }
@@ -198,11 +199,12 @@ 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
- * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
- * @key: address where result is stored.
- * @rw: mapping needs to be read/write (values: VERIFY_READ, VERIFY_WRITE)
+ * get_futex_key() - Get parameters which are the keys for a futex
+ * @uaddr:	virtual address of the futex
+ * @fshared:	0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
+ * @key:	address where result is stored.
+ * @rw:		mapping needs to be read/write (values: VERIFY_READ,
+ * 		VERIFY_WRITE)
  *
  * Returns a negative error code or 0
  * The key words are stored in *key on success.
@@ -288,8 +290,8 @@ void put_futex_key(int fshared, union futex_key *key)
 	drop_futex_key_refs(key);
 }
 
-/*
- * fault_in_user_writeable - fault in user address and verify RW access
+/**
+ * fault_in_user_writeable() - Fault in user address and verify RW access
  * @uaddr:	pointer to faulting user space address
  *
  * Slow path to fixup the fault we just took in the atomic write
@@ -309,8 +311,8 @@ static int fault_in_user_writeable(u32 __user *uaddr)
 
 /**
  * futex_top_waiter() - Return the highest priority waiter on a futex
- * @hb:     the hash bucket the futex_q's reside in
- * @key:    the futex key (to distinguish it from other futex futex_q's)
+ * @hb:		the hash bucket the futex_q's reside in
+ * @key:	the futex key (to distinguish it from other futex futex_q's)
  *
  * Must be called with the hb lock held.
  */
@@ -588,7 +590,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 }
 
 /**
- * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
+ * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
  * @uaddr:		the pi futex user address
  * @hb:			the pi futex hash bucket
  * @key:		the futex key associated with uaddr and hb
@@ -915,8 +917,8 @@ retry:
 	hb1 = hash_futex(&key1);
 	hb2 = hash_futex(&key2);
 
-	double_lock_hb(hb1, hb2);
 retry_private:
+	double_lock_hb(hb1, hb2);
 	op_ret = futex_atomic_op_inuser(op, uaddr2);
 	if (unlikely(op_ret < 0)) {
 
@@ -1011,9 +1013,9 @@ void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
 
 /**
  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
- * q:	the futex_q
- * key:	the key of the requeue target futex
- * hb:  the hash_bucket of the requeue target futex
+ * @q:		the futex_q
+ * @key:	the key of the requeue target futex
+ * @hb:		the hash_bucket of the requeue target futex
  *
  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
@@ -1027,7 +1029,6 @@ static inline
 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
 			   struct futex_hash_bucket *hb)
 {
-	drop_futex_key_refs(&q->key);
 	get_futex_key_refs(key);
 	q->key = *key;
 
@@ -1225,6 +1226,7 @@ retry_private:
 		 */
 		if (ret == 1) {
 			WARN_ON(pi_state);
+			drop_count++;
 			task_count++;
 			ret = get_futex_value_locked(&curval2, uaddr2);
 			if (!ret)
@@ -1303,6 +1305,7 @@ retry_private:
 			if (ret == 1) {
 				/* We got the lock. */
 				requeue_pi_wake_futex(this, &key2, hb2);
+				drop_count++;
 				continue;
 			} else if (ret) {
 				/* -EDEADLK */
@@ -1350,6 +1353,25 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
 	return hb;
 }
 
+static inline void
+queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
+{
+	spin_unlock(&hb->lock);
+	drop_futex_key_refs(&q->key);
+}
+
+/**
+ * queue_me() - Enqueue the futex_q on the futex_hash_bucket
+ * @q:	The futex_q to enqueue
+ * @hb:	The destination hash bucket
+ *
+ * The hb->lock must be held by the caller, and is released here. A call to
+ * queue_me() is typically paired with exactly one call to unqueue_me().  The
+ * exceptions involve the PI related operations, which may use unqueue_me_pi()
+ * or nothing if the unqueue is done as part of the wake process and the unqueue
+ * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
+ * an example).
+ */
 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 {
 	int prio;
@@ -1373,19 +1395,17 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 	spin_unlock(&hb->lock);
 }
 
-static inline void
-queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
-{
-	spin_unlock(&hb->lock);
-	drop_futex_key_refs(&q->key);
-}
-
-/*
- * queue_me and unqueue_me must be called as a pair, each
- * exactly once.  They are called with the hashed spinlock held.
+/**
+ * unqueue_me() - Remove the futex_q from its futex_hash_bucket
+ * @q:	The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
+ * be paired with exactly one earlier call to queue_me().
+ *
+ * Returns:
+ *   1 - if the futex_q was still queued (and we removed unqueued it)
+ *   0 - if the futex_q was already removed by the waking thread
  */
-
-/* Return 1 if we were still queued (ie. 0 means we were woken) */
 static int unqueue_me(struct futex_q *q)
 {
 	spinlock_t *lock_ptr;
@@ -1638,17 +1658,14 @@ out:
 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
 				struct hrtimer_sleeper *timeout)
 {
-	queue_me(q, hb);
-
 	/*
-	 * There might have been scheduling since the queue_me(), as we
-	 * cannot hold a spinlock across the get_user() in case it
-	 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
-	 * queueing ourselves into the futex hash. This code thus has to
-	 * rely on the futex_wake() code removing us from hash when it
-	 * wakes us up.
+	 * The task state is guaranteed to be set before another task can
+	 * wake it. set_current_state() is implemented using set_mb() and
+	 * queue_me() calls spin_unlock() upon completion, both serializing
+	 * access to the hash list and forcing another memory barrier.
 	 */
 	set_current_state(TASK_INTERRUPTIBLE);
+	queue_me(q, hb);
 
 	/* Arm the timer */
 	if (timeout) {
@@ -1658,8 +1675,8 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
 	}
 
 	/*
-	 * !plist_node_empty() is safe here without any lock.
-	 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
+	 * If we have been removed from the hash list, then another task
+	 * has tried to wake us, and we can skip the call to schedule().
 	 */
 	if (likely(!plist_node_empty(&q->list))) {
 		/*
@@ -1776,6 +1793,7 @@ static int futex_wait(u32 __user *uaddr, int fshared,
 					     current->timer_slack_ns);
 	}
 
+retry:
 	/* Prepare to wait on uaddr. */
 	ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
 	if (ret)
@@ -1793,9 +1811,14 @@ static int futex_wait(u32 __user *uaddr, int fshared,
 		goto out_put_key;
 
 	/*
-	 * We expect signal_pending(current), but another thread may
-	 * have handled it for us already.
+	 * We expect signal_pending(current), but we might be the
+	 * victim of a spurious wakeup as well.
 	 */
+	if (!signal_pending(current)) {
+		put_futex_key(fshared, &q.key);
+		goto retry;
+	}
+
 	ret = -ERESTARTSYS;
 	if (!abs_time)
 		goto out_put_key;
@@ -2102,11 +2125,12 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
 		 * Unqueue the futex_q and determine which it was.
 		 */
 		plist_del(&q->list, &q->list.plist);
-		drop_futex_key_refs(&q->key);
 
+		/* Handle spurious wakeups gracefully */
+		ret = -EWOULDBLOCK;
 		if (timeout && !timeout->task)
 			ret = -ETIMEDOUT;
-		else
+		else if (signal_pending(current))
 			ret = -ERESTARTNOINTR;
 	}
 	return ret;
@@ -2302,9 +2326,9 @@ out:
  */
 
 /**
- * sys_set_robust_list - set the robust-futex list head of a task
- * @head: pointer to the list-head
- * @len: length of the list-head, as userspace expects
+ * sys_set_robust_list() - Set the robust-futex list head of a task
+ * @head:	pointer to the list-head
+ * @len:	length of the list-head, as userspace expects
  */
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 		size_t, len)
@@ -2323,10 +2347,10 @@ SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 }
 
 /**
- * sys_get_robust_list - get the robust-futex list head of a task
- * @pid: pid of the process [zero for current task]
- * @head_ptr: pointer to a list-head pointer, the kernel fills it in
- * @len_ptr: pointer to a length field, the kernel fills in the header size
+ * sys_get_robust_list() - Get the robust-futex list head of a task
+ * @pid:	pid of the process [zero for current task]
+ * @head_ptr:	pointer to a list-head pointer, the kernel fills it in
+ * @len_ptr:	pointer to a length field, the kernel fills in the header size
  */
 SYSCALL_DEFINE3(get_robust_list, int, pid,
 		struct robust_list_head __user * __user *, head_ptr,