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

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Date:   Mon, 25 Oct 2021 21:14:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+9738c8815b375ce482a1@...kaller.appspotmail.com,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.14 090/169] blk-cgroup: blk_cgroup_bio_start() should use irq-safe operations on blkg->iostat_cpu

From: Tejun Heo <tj@...nel.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@...r.kernel.org # v5.13+
Reported-by: syzbot+9738c8815b375ce482a1@...kaller.appspotmail.com
Signed-off-by: Tejun Heo <tj@...nel.org>
Link: https://lore.kernel.org/r/YWi7NrQdVlxD6J9W@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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();