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

[Tejun Heo]

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@xxxxxxxxxxxxxxx # v5.13+
Reported-by: syzbot+9738c8815b375ce482a1@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 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();