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mm/page_io: don't nest queue_lock under rcu in bio_associate_blkg_from_page()

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Take a css reference under RCU, drop RCU, and then associate the bio with
the blkg. This avoids nesting queue_lock under RCU and prepares to protect
blkcg with blkcg_mutex instead of queue_lock.

Use css_tryget() instead of css_tryget_online() so swap writeback for
pages charged to a dying memcg still passes the dying css to
bio_associate_blkg_from_css(). That preserves the existing closest-live
ancestor fallback instead of charging those bios to the root blkg.

Signed-off-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/c910d2c39d3ec97f67de68af636a52394342d55f.1780621988.git.yukuai@fygo.io
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2026-06-08 11:42:48 +08:00 committed by Jens Axboe
parent 4cfd7c1cff
commit f928145cbc
1 changed files with 6 additions and 1 deletions
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7
mm/page_io.c
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@ -317,8 +317,13 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
rcu_read_lock();
memcg = folio_memcg(folio);
css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
bio_associate_blkg_from_css(bio, css);
if (!css || !css_tryget(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)