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blk-cgroup: protect iterating blkgs with blkcg->lock in blkcg_print_stat()

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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 <yukuai@fygo.io>
Link: https://patch.msgid.link/05799877e720dcd300e2ddd4625e8e162959d7cc.1780621988.git.yukuai@fygo.io
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2026-06-08 11:42:42 +08:00 committed by Jens Axboe
parent 8a901e629e
commit 25656304da
1 changed files with 3 additions and 6 deletions
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9
block/blk-cgroup.c
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@ -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;
}