diff mbox series

[5.15,7/9] xfs: fix soft lockup via spinning in filestream ag selection loop

Message ID 20220819181431.4113819-8-leah.rumancik@gmail.com (mailing list archive)
State Superseded
Headers show
Series xfs stable candidate patches for 5.15.y (part 4) | expand

Commit Message

Leah Rumancik Aug. 19, 2022, 6:14 p.m. UTC 
From: Brian Foster <bfoster@redhat.com>

[ Upstream commit f650df7171b882dca737ddbbeb414100b31f16af ]

The filestream AG selection loop uses pagf data to aid in AG
selection, which depends on pagf initialization. If the in-core
structure is not initialized, the caller invokes the AGF read path
to do so and carries on. If another task enters the loop and finds
a pagf init already in progress, the AGF read returns -EAGAIN and
the task continues the loop. This does not increment the current ag
index, however, which means the task spins on the current AGF buffer
until unlocked.

If the AGF read I/O submitted by the initial task happens to be
delayed for whatever reason, this results in soft lockup warnings
via the spinning task. This is reproduced by xfs/170. To avoid this
problem, fix the AGF trylock failure path to properly iterate to the
next AG. If a task iterates all AGs without making progress, the
trylock behavior is dropped in favor of blocking locks and thus a
soft lockup is no longer possible.

Fixes: f48e2df8a877ca1c ("xfs: make xfs_*read_agf return EAGAIN to ALLOC_FLAG_TRYLOCK callers")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_filestream.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index 6a3ce0f6dc9e..be9bcf8a1f99 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -128,11 +128,12 @@  xfs_filestream_pick_ag(
 		if (!pag->pagf_init) {
 			err = xfs_alloc_pagf_init(mp, NULL, ag, trylock);
 			if (err) {
-				xfs_perag_put(pag);
-				if (err != -EAGAIN)
+				if (err != -EAGAIN) {
+					xfs_perag_put(pag);
 					return err;
+				}
 				/* Couldn't lock the AGF, skip this AG. */
-				continue;
+				goto next_ag;
 			}
 		}