btrfs: add comments to barriers before waitqueue_active

Reduce number of undocumented barriers out there.

Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 52170cf1757e..071005f008c1 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -345,6 +345,9 @@ int btrfs_dec_test_first_ordered_pending(struct inode *inode,
 
         if (entry->bytes_left == 0) {
                 ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
+                /*
+                 * Implicit memory barrier after test_and_set_bit
+                 */
                 if (waitqueue_active(&entry->wait))
                         wake_up(&entry->wait);
         } else {
@@ -409,6 +412,9 @@ have_entry:
 
         if (entry->bytes_left == 0) {
                 ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
+                /*
+                 * Implicit memory barrier after test_and_set_bit
+                 */
                 if (waitqueue_active(&entry->wait))
                         wake_up(&entry->wait);
         } else {