5.4-stable review patch. If anyone has any objections, please let me know.
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From: Ojaswin Mujoo ojaswin@linux.ibm.com
[ Upstream commit ac6f420291b3fee1113f21d612fa88b628afab5b ]
One of the paths quota writeback is called from is:
freeze_super() sync_filesystem() ext4_sync_fs() dquot_writeback_dquots()
Since we currently don't always flush the quota_release_work queue in this path, we can end up with the following race:
1. dquot are added to releasing_dquots list during regular operations. 2. FS Freeze starts, however, this does not flush the quota_release_work queue. 3. Freeze completes. 4. Kernel eventually tries to flush the workqueue while FS is frozen which hits a WARN_ON since transaction gets started during frozen state:
ext4_journal_check_start+0x28/0x110 [ext4] (unreliable) __ext4_journal_start_sb+0x64/0x1c0 [ext4] ext4_release_dquot+0x90/0x1d0 [ext4] quota_release_workfn+0x43c/0x4d0
Which is the following line:
WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE);
Which ultimately results in generic/390 failing due to dmesg noise. This was detected on powerpc machine 15 cores.
To avoid this, make sure to flush the workqueue during dquot_writeback_dquots() so we dont have any pending workitems after freeze.
Reported-by: Disha Goel disgoel@linux.ibm.com CC: stable@vger.kernel.org Fixes: dabc8b207566 ("quota: fix dqput() to follow the guarantees dquot_srcu should provide") Reviewed-by: Baokun Li libaokun1@huawei.com Signed-off-by: Ojaswin Mujoo ojaswin@linux.ibm.com Signed-off-by: Jan Kara jack@suse.cz Link: https://patch.msgid.link/20241121123855.645335-2-ojaswin@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/quota/dquot.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 14c0dd5b65a43..42c2ac0cc8fc9 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -681,6 +681,8 @@ int dquot_writeback_dquots(struct super_block *sb, int type)
WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));
+ flush_delayed_work("a_release_work); + for (cnt = 0; cnt < MAXQUOTAS; cnt++) { if (type != -1 && cnt != type) continue;