On Fri, Feb 19, 2021 at 03:56:58PM +1100, Dave Chinner wrote:

On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:

quoted

On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:

quoted

fstest xfs/167 produced a lockdep splat that complained about a
nested transaction acquiring freeze protection during an eofblocks
scan. Drop freeze protection around the block reclaim scan in the
transaction allocation code to avoid this problem.

Signed-off-by: Brian Foster <redacted>

...

quoted

quoted

 fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 44f72c09c203..c32c62d3b77a 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c

...

quoted

quoted

@@ -288,19 +289,27 @@ xfs_trans_alloc(
 	INIT_LIST_HEAD(&tp->t_dfops);
 	tp->t_firstblock = NULLFSBLOCK;
 
+retry:
 	error = xfs_trans_reserve(tp, resp, blocks, rtextents);
-	if (error == -ENOSPC) {
+	if (error == -ENOSPC && !retried) {
 		/*
 		 * We weren't able to reserve enough space for the transaction.
 		 * Flush the other speculative space allocations to free space.
 		 * Do not perform a synchronous scan because callers can hold
 		 * other locks.
 		 */
+		retried = true;
+		if (!(flags & XFS_TRANS_NO_WRITECOUNT))
+			sb_end_intwrite(mp->m_super);
 		error = xfs_blockgc_free_space(mp, NULL);
-		if (!error)
-			error = xfs_trans_reserve(tp, resp, blocks, rtextents);
-	}
-	if (error) {
+		if (error) {
+			kmem_cache_free(xfs_trans_zone, tp);
+			return error;
+		}

This seems dangerous to me. If xfs_trans_reserve() adds anything to
the transaction even if it fails, this will fail to free it. e.g.
xfs_log_reserve() call allocate a ticket and attach it to the
transaction and *then fail*. This code will now leak that ticket.

xfs_trans_reserve() ungrants the log ticket (which frees it, at least in
the allocation case) and disassociates from the transaction on error, so
I don't see how this causes any problems.

Brian

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com