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[v2,1/3] btrfs: introduce conditional wakeup helpers

Message ID 0ed05bc9b62df9f3e9acd2cb0a2541d7aaf2a94a.1524575208.git.dsterba@suse.com (mailing list archive)
State New, archived
Headers show

Commit Message

David Sterba April 24, 2018, 1:10 p.m. UTC 
Add convenience wrappers for the waitqueue management that involves
memory barriers to prevent deadlocks. The helpers will let us remove
barriers and the necessary comments in several places.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/ctree.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
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Patch

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2771cc56a622..1389942f3be1 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3765,4 +3765,26 @@  static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info)
 	return 0;
 }
 
+static inline void cond_wake_up(struct wait_queue_head *wq)
+{
+	/*
+	 * This implies a full smp_mb barrier, see comments for
+	 * waitqueue_active why.
+	 */
+	if (wq_has_sleeper(wq))
+		wake_up(wq);
+}
+
+static inline void cond_wake_up_nomb(struct wait_queue_head *wq)
+{
+	/*
+	 * Special case for conditional wakeup where the barrier required for
+	 * waitqueue_active is implied by some of the preceding code. Eg. one
+	 * of such atomic operations (atomic_dec_and_return, ...), or a
+	 * unlock/lock sequence, etc.
+	 */
+	if (waitqueue_active(wq))
+		wake_up(wq);
+}
+
 #endif