Re: [syzbot] [btrfs?] WARNING: bad unlock balance in btrfs_direct_write

[Edward Adam Davis]

btrfs_sync_file didn't use skip_ilock to split up_write and btrfs_inode_unlock

#syz test: upstream e4fc196f5ba3

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 9f10a9f23fcc..9914419f3b7d 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1868,7 +1868,10 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 
 out_release_extents:
 	btrfs_release_log_ctx_extents(&ctx);
-	btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);
+	if (skip_ilock)
+		up_write(&inode->i_mmap_lock);
+	else
+		btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);
 	goto out;
 }