btrfs: comment the rest of implicit barriers before waitqueue_active

There are atomic operations that imply the barrier for waitqueue_active
mixed in an if-condition.

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

5 files changed, 22 insertions, 0 deletions

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index a2ae42720a6a..e0941fbb913c 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -463,6 +463,10 @@ static int __btrfs_add_delayed_deletion_item(struct btrfs_delayed_node *node,
 static void finish_one_item(struct btrfs_delayed_root *delayed_root)
 {
         int seq = atomic_inc_return(&delayed_root->items_seq);
+
+        /*
+         * atomic_dec_return implies a barrier for waitqueue_active
+         */
         if ((atomic_dec_return(&delayed_root->items) <
             BTRFS_DELAYED_BACKGROUND || seq % BTRFS_DELAYED_BATCH == 0) &&
             waitqueue_active(&delayed_root->wait))
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 295795aebe0b..379526ffd84d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -802,6 +802,9 @@ static void run_one_async_done(struct btrfs_work *work)
         limit = btrfs_async_submit_limit(fs_info);
         limit = limit * 2 / 3;
 
+        /*
+         * atomic_dec_return implies a barrier for waitqueue_active
+         */
         if (atomic_dec_return(&fs_info->nr_async_submits) < limit &&
             waitqueue_active(&fs_info->async_submit_wait))
                 wake_up(&fs_info->async_submit_wait);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 611b66d73e80..7be4abe25e06 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1096,6 +1096,9 @@ static noinline void async_cow_submit(struct btrfs_work *work)
         nr_pages = (async_cow->end - async_cow->start + PAGE_CACHE_SIZE) >>
                 PAGE_CACHE_SHIFT;
 
+        /*
+         * atomic_sub_return implies a barrier for waitqueue_active
+         */
         if (atomic_sub_return(nr_pages, &root->fs_info->async_delalloc_pages) <
             5 * 1024 * 1024 &&
             waitqueue_active(&root->fs_info->async_submit_wait))
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 03f8630dbaf2..8077461fc56a 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -79,6 +79,9 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
                 write_lock(&eb->lock);
                 WARN_ON(atomic_read(&eb->spinning_writers));
                 atomic_inc(&eb->spinning_writers);
+                /*
+                 * atomic_dec_and_test implies a barrier for waitqueue_active
+                 */
                 if (atomic_dec_and_test(&eb->blocking_writers) &&
                     waitqueue_active(&eb->write_lock_wq))
                         wake_up(&eb->write_lock_wq);
@@ -86,6 +89,9 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
                 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
                 read_lock(&eb->lock);
                 atomic_inc(&eb->spinning_readers);
+                /*
+                 * atomic_dec_and_test implies a barrier for waitqueue_active
+                 */
                 if (atomic_dec_and_test(&eb->blocking_readers) &&
                     waitqueue_active(&eb->read_lock_wq))
                         wake_up(&eb->read_lock_wq);
@@ -229,6 +235,9 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
         }
         btrfs_assert_tree_read_locked(eb);
         WARN_ON(atomic_read(&eb->blocking_readers) == 0);
+        /*
+         * atomic_dec_and_test implies a barrier for waitqueue_active
+         */
         if (atomic_dec_and_test(&eb->blocking_readers) &&
             waitqueue_active(&eb->read_lock_wq))
                 wake_up(&eb->read_lock_wq);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6fc735869c18..ff3527192409 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -345,6 +345,9 @@ loop_lock:
                 pending = pending->bi_next;
                 cur->bi_next = NULL;
 
+                /*
+                 * atomic_dec_return implies a barrier for waitqueue_active
+                 */
                 if (atomic_dec_return(&fs_info->nr_async_bios) < limit &&
                     waitqueue_active(&fs_info->async_submit_wait))
                         wake_up(&fs_info->async_submit_wait);