2021-10-15 07:21:26

by Tejun Heo

Subject: [PATCH block-5.15] blk-cgroup: blk_cgroup_bio_start() should use irq-safe operations on blkg->iostat_cpu

c3df5fb57fe8 ("cgroup: rstat: fix A-A deadlock on 32bit around
u64_stats_sync") made u64_stats updates irq-safe to avoid A-A deadlocks.
Unfortunately, the conversion missed one in blk_cgroup_bio_start(). Fix it.

Fixes: 2d146aa3aa84 ("mm: memcontrol: switch to rstat")
Cc: [email protected] # v5.13+
Reported-by: [email protected]
Signed-off-by: Tejun Heo <[email protected]>
---
block/blk-cgroup.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 31fe9be179d99..7d0509d9f4ea8 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1906,10 +1906,11 @@ void blk_cgroup_bio_start(struct bio *bio)
{
int rwd = blk_cgroup_io_type(bio), cpu;
struct blkg_iostat_set *bis;
+ unsigned long flags;

cpu = get_cpu();
bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
- u64_stats_update_begin(&bis->sync);
+ flags = u64_stats_update_begin_irqsave(&bis->sync);

/*
* If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
@@ -1921,7 +1922,7 @@ void blk_cgroup_bio_start(struct bio *bio)
}
bis->cur.ios[rwd]++;

- u64_stats_update_end(&bis->sync);
+ u64_stats_update_end_irqrestore(&bis->sync, flags);
if (cgroup_subsys_on_dfl(io_cgrp_subsys))
cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
put_cpu();

2021-10-18 03:47:29

by Jens Axboe

Subject: Re: [PATCH block-5.15] blk-cgroup: blk_cgroup_bio_start() should use irq-safe operations on blkg->iostat_cpu

On Thu, 14 Oct 2021 13:20:22 -1000, Tejun Heo wrote:
> c3df5fb57fe8 ("cgroup: rstat: fix A-A deadlock on 32bit around
> u64_stats_sync") made u64_stats updates irq-safe to avoid A-A deadlocks.
> Unfortunately, the conversion missed one in blk_cgroup_bio_start(). Fix it.
>
>

Applied, thanks!

[1/1] blk-cgroup: blk_cgroup_bio_start() should use irq-safe operations on blkg->iostat_cpu
commit: 5370b0f49078203acf3c064b634a09707167a864

Best regards,
--
Jens Axboe