From 25656304dabd26198ec69460c594a19d086ef099 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Mon, 8 Jun 2026 11:42:42 +0800 Subject: [PATCH] blk-cgroup: protect iterating blkgs with blkcg->lock in blkcg_print_stat() blkcg_print_one_stat() will be called for each blkg: - access blkg->iostat, which is freed from rcu callback blkg_free_workfn(); - access policy data from pd_stat_fn(), which is freed from pd_free_fn(), while pd_free_fn() can be called by removing blkcg or deactivating policy; Take blkcg->lock while iterating so the blkgs stay online and both blkg->iostat and policy data for activated policies stay valid. Use irq-safe locking because blkcg->lock can be nested under q->queue_lock, which is used from IRQ completion paths. Prepare to convert protecting blkgs from request_queue with mutex. Signed-off-by: Yu Kuai Link: https://patch.msgid.link/05799877e720dcd300e2ddd4625e8e162959d7cc.1780621988.git.yukuai@fygo.io Signed-off-by: Jens Axboe --- block/blk-cgroup.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index ee076ab795d3..c991c263cb5a 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1191,13 +1191,10 @@ static int blkcg_print_stat(struct seq_file *sf, void *v) else css_rstat_flush(&blkcg->css); - rcu_read_lock(); - hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) { - spin_lock_irq(&blkg->q->queue_lock); + guard(spinlock_irq)(&blkcg->lock); + hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) blkcg_print_one_stat(blkg, sf); - spin_unlock_irq(&blkg->q->queue_lock); - } - rcu_read_unlock(); + return 0; }