From 110a21feedd78d398598d91be57db60e19b76fe0 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Mon, 26 Feb 2018 15:43:18 +0100 Subject: [PATCH] btrfs: introduce conditional wakeup helpers 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 Signed-off-by: David Sterba --- fs/btrfs/ctree.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 954bfb5..3d6b2dc 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3755,4 +3755,26 @@ 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 -- 2.7.4