From f928145cbcb52544203808f159461d0a25543df7 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Mon, 8 Jun 2026 11:42:48 +0800 Subject: [PATCH] mm/page_io: don't nest queue_lock under rcu in bio_associate_blkg_from_page() 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 Link: https://patch.msgid.link/c910d2c39d3ec97f67de68af636a52394342d55f.1780621988.git.yukuai@fygo.io Signed-off-by: Jens Axboe --- 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 a59b73f8bdd9..c96d3e4cf872 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -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)