This is a note to let you know that I've just added the patch titled
ext4: fix dead loop in ext4_mb_new_blocks
to the 5.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ext4-fix-dead-loop-in-ext4_mb_new_blocks.patch
and it can be found in the queue-5.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6e2d9385db271ed7e66a21ee7d6e76173fca6221
Author: Ye Bin <yebin10@xxxxxxxxxx>
Date: Wed Sep 16 19:38:59 2020 +0800
ext4: fix dead loop in ext4_mb_new_blocks
[ Upstream commit 70022da804f0f3f152115688885608c39182082e ]
As we test disk offline/online with running fsstress, we find fsstress
process is keeping running state.
kworker/u32:3-262 [004] ...1 140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114
....
kworker/u32:3-262 [004] ...1 140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114
ext4_mb_new_blocks
repeat:
ext4_mb_discard_preallocations_should_retry(sb, ac, &seq)
freed = ext4_mb_discard_preallocations
ext4_mb_discard_group_preallocations
this_cpu_inc(discard_pa_seq);
---> freed == 0
seq_retry = ext4_get_discard_pa_seq_sum
for_each_possible_cpu(__cpu)
__seq += per_cpu(discard_pa_seq, __cpu);
if (seq_retry != *seq) {
*seq = seq_retry;
ret = true;
}
As we see seq_retry is sum of discard_pa_seq every cpu, if
ext4_mb_discard_group_preallocations return zero discard_pa_seq in this
cpu maybe increase one, so condition "seq_retry != *seq" have always
been met.
Ritesh Harjani suggest to in ext4_mb_discard_group_preallocations function we
only increase discard_pa_seq when there is some PA to free.
Fixes: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling")
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200916113859.1556397-3-yebin10@xxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 132c118d12e15..ff47347012f4b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4189,7 +4189,6 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
INIT_LIST_HEAD(&list);
repeat:
ext4_lock_group(sb, group);
- this_cpu_inc(discard_pa_seq);
list_for_each_entry_safe(pa, tmp,
&grp->bb_prealloc_list, pa_group_list) {
spin_lock(&pa->pa_lock);
@@ -4206,6 +4205,9 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
/* seems this one can be freed ... */
ext4_mb_mark_pa_deleted(sb, pa);
+ if (!free)
+ this_cpu_inc(discard_pa_seq);
+
/* we can trust pa_free ... */
free += pa->pa_free;
