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.
Signed-off-by: David Sterba <dste...@suse.com>
---
fs/btrfs/ctree.h | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index bf545e7552b8..c9827a1b676d 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3748,4 +3748,27 @@ static inline int btrfs_is_testing(struct btrfs_fs_info
*fs_info)
#endif
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
--
2.16.2
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