btrfs: disable strict file flushes for renames and truncates

Truncates and renames are often used to replace old versions of a file
with new versions.  Applications often expect this to be an atomic
replacement, even if they haven't done anything to make sure the new
version is fully on disk.

Btrfs has strict flushing in place to make sure that renaming over an
old file with a new file will fully flush out the new file before
allowing the transaction commit with the rename to complete.

This ordering means the commit code needs to be able to lock file pages,
and there are a few paths in the filesystem where we will try to end a
transaction with the page lock held.  It's rare, but these things can
deadlock.

This patch removes the ordered flushes and switches to a best effort
filemap_flush like ext4 uses. It's not perfect, but it should fix the
deadlocks.

Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 1 insertions, 25 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 1f2b99c..d3afac2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1838,33 +1838,9 @@ out:
 
 int btrfs_release_file(struct inode *inode, struct file *filp)
 {
-	/*
-	 * ordered_data_close is set by settattr when we are about to truncate
-	 * a file from a non-zero size to a zero size.  This tries to
-	 * flush down new bytes that may have been written if the
-	 * application were using truncate to replace a file in place.
-	 */
-	if (test_and_clear_bit(BTRFS_INODE_ORDERED_DATA_CLOSE,
-			       &BTRFS_I(inode)->runtime_flags)) {
-		struct btrfs_trans_handle *trans;
-		struct btrfs_root *root = BTRFS_I(inode)->root;
-
-		/*
-		 * We need to block on a committing transaction to keep us from
-		 * throwing a ordered operation on to the list and causing
-		 * something like sync to deadlock trying to flush out this
-		 * inode.
-		 */
-		trans = btrfs_start_transaction(root, 0);
-		if (IS_ERR(trans))
-			return PTR_ERR(trans);
-		btrfs_add_ordered_operation(trans, BTRFS_I(inode)->root, inode);
-		btrfs_end_transaction(trans, root);
-		if (inode->i_size > BTRFS_ORDERED_OPERATIONS_FLUSH_LIMIT)
-			filemap_flush(inode->i_mapping);
-	}
 	if (filp->private_data)
 		btrfs_ioctl_trans_end(filp);
+	filemap_flush(inode->i_mapping);
 	return 0;
 }