[PATCH] radix-tree: Avoid false wakeups when waiting for exceptional entry lock

[Jan Kara]

Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 lib/radix-tree.c | 42 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 5 deletions(-)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index a97231ab66f0..be9763dd9de5 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -1522,6 +1522,28 @@ static inline void * unlock_slot(void **v)
 	return (void*)(*l &= ~1UL);
 }
 
+struct exceptional_entry_key {
+	struct radix_tree_root *root;
+	unsigned long index;
+};
+
+struct wait_exceptional_entry_queue {
+	wait_queue_t wait;
+	struct exceptional_entry_key key;
+};
+
+static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned mode,
+				       int sync, void *keyp)
+{
+	struct exceptional_entry_key *key = keyp;
+	struct wait_exceptional_entry_queue *ewait =
+		container_of(wait, struct wait_exceptional_entry_queue, wait);
+
+	if (key->root != ewait->key.root || key->index != ewait->key.index)
+		return 0;
+	return autoremove_wake_function(wait, mode, sync, NULL);
+}
+
 /**
  *	radix_tree_lookup_lock - lookup and lock exceptional entry if found
  *	@root:		radix tree root
@@ -1540,7 +1562,12 @@ void *radix_tree_lookup_lock(struct radix_tree_root *root, unsigned long index,
 			     wait_queue_head_t *wq, spinlock_t *lock)
 {
 	void *ret, **slot;
-	DEFINE_WAIT(wait);
+	struct wait_exceptional_entry_queue wait;
+
+	init_wait(&wait.wait);
+	wait.wait.func = wake_exceptional_entry_func;
+	wait.key.root = root;
+	wait.key.index = index;
 
 	for (;;) {
 		ret = __radix_tree_lookup(root, index, NULL, &slot);
@@ -1548,10 +1575,10 @@ void *radix_tree_lookup_lock(struct radix_tree_root *root, unsigned long index,
 			return ret;
 		if (!slot_locked(slot))
 			return lock_slot(slot);
-		prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
+		prepare_to_wait_exclusive(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
 		spin_unlock(lock);
 		schedule();
-		finish_wait(wq, &wait);
+		finish_wait(wq, &wait.wait);
 		spin_lock(lock);
 	}
 }
@@ -1579,7 +1606,12 @@ void radix_tree_unlock(struct radix_tree_root *root, unsigned long index,
 		return;
 	unlock_slot(slot);
 
-	if (waitqueue_active(wq))
-		wake_up(wq);
+	if (waitqueue_active(wq)) {
+		struct exceptional_entry_key key;
+
+		key.root = root;
+		key.index = index;
+		__wake_up(wq, TASK_NORMAL, 1, &key);
+	}
 }
 EXPORT_SYMBOL(radix_tree_unlock);
-- 
2.6.2


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