linux-kernel - [PATCH 05/10] mm/page_io: don't nest queue_lock under rcu in bio_associate_blkg_from

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Message-Id: <20250925081525.700639-6-yukuai1@huaweicloud.com>
Date: Thu, 25 Sep 2025 16:15:20 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: tj@...nel.org,
	ming.lei@...hat.com,
	nilay@...ux.ibm.com,
	hch@....de,
	josef@...icpanda.com,
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Cc: cgroups@...r.kernel.org,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
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	yukuai3@...wei.com,
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	johnny.chenyi@...wei.com
Subject: [PATCH 05/10] mm/page_io: don't nest queue_lock under rcu in bio_associate_blkg_from_page()

From: Yu Kuai <yukuai3@...wei.com>

Prepare to convert protecting blkcg with blkcg_mutex instead of
queue_lock.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 mm/page_io.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index a2056a5ecb13..4f4cc9370573 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -313,8 +313,13 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
 
 	rcu_read_lock();
 	css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
-	bio_associate_blkg_from_css(bio, css);
+	if (!css || !css_tryget_online(css))
+		css = NULL;
 	rcu_read_unlock();
+
+	bio_associate_blkg_from_css(bio, css);
+	if (css)
+		css_put(css);
 }
 #else
 #define bio_associate_blkg_from_page(bio, folio)		do { } while (0)
-- 
2.39.2