btrfs: update comment for btrfs_set_inode_full_sync() about locking

Nowadays we have a lock used to synchronize mmap writes with reflink and
fsync operations (struct btrfs_inode::i_mmap_lock), so update the comment
for btrfs_set_inode_full_sync() to mention that it can also be called
while holding that mmap lock. Besides being a valid alternative to the
inode's VFS lock, we already have the extent map shrinker using that mmap
lock instead.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 9a87ada7fe52..91c994b569f3 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -381,9 +381,11 @@ static inline void btrfs_set_inode_last_sub_trans(struct btrfs_inode *inode)
 }
 
 /*
- * Should be called while holding the inode's VFS lock in exclusive mode or in a
- * context where no one else can access the inode concurrently (during inode
- * creation or when loading an inode from disk).
+ * Should be called while holding the inode's VFS lock in exclusive mode, or
+ * while holding the inode's mmap lock (struct btrfs_inode::i_mmap_lock) in
+ * either shared or exclusive mode, or in a context where no one else can access
+ * the inode concurrently (during inode creation or when loading an inode from
+ * disk).
  */
 static inline void btrfs_set_inode_full_sync(struct btrfs_inode *inode)
 {