From: Ye Bin yebin10@huawei.com
[ 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@huawei.com Reviewed-by: Jan Kara jack@suse.cz Reviewed-by: Ritesh Harjani riteshh@linux.ibm.com Link: https://lore.kernel.org/r/20200916113859.1556397-3-yebin10@huawei.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Sasha Levin sashal@kernel.org --- fs/ext4/mballoc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index e88eff999bd15..787a894f5d1da 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -4066,7 +4066,6 @@ 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); @@ -4083,6 +4082,9 @@ 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;