[PATCH 5.14 090/169] blk-cgroup: blk_cgroup_bio_start() should use irq-safe operations on blkg->iostat_cpu

Greg Kroah-Hartman
2021-10-25T19:53:03Z

From: Tejun Heo <tj@kernel.org>

commit 5370b0f49078203acf3c064b634a09707167a864 upstream.

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: stable@vger.kernel.org # v5.13+
Reported-by: syzbot+9738c8815b375ce482a1@syzkaller.appspotmail.com
Signed-off-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/YWi7NrQdVlxD6J9W@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/blk-cgroup.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1916,10 +1916,11 @@ void blk_cgroup_bio_start(struct bio *bi
{
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
@@ -1931,7 +1932,7 @@ void blk_cgroup_bio_start(struct bio *bi
}
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();