From f650df7171b882dca737ddbbeb414100b31f16af Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Tue, 26 Apr 2022 13:34:54 +1000 Subject: [PATCH] xfs: fix soft lockup via spinning in filestream ag selection loop 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 Reviewed-by: Darrick J. Wong Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner --- fs/xfs/xfs_filestream.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c index 6a3ce0f..be9bcf8 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; } } -- 2.7.4