Re: [PATCH] blk-cgroup: prevent rcu_sched detected stalls warnings while iterating blkgs
From: Tejun Heo <hidden>
Date: 2021-07-06 17:56:36
Also in:
linux-block, lkml
Hello, Yu. On Fri, Jul 02, 2021 at 12:04:44PM +0800, Yu Kuai wrote:
blkcg_activate_policy() and blkcg_deactivate_policy() might have the same problem, fix them the same way.
Given that these are basically only called from module init/exit paths, let's leave them alone for now.
+#define BLKG_BATCH_OP_NUM 64
Can we do BLKG_DESTRY_BATCH_SIZE instead?
quoted hunk ↗ jump to hunk
static void blkg_destroy_all(struct request_queue *q) { struct blkcg_gq *blkg, *n; + int count = BLKG_BATCH_OP_NUM; +restart: spin_lock_irq(&q->queue_lock); list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) { struct blkcg *blkcg = blkg->blkcg;@@ -430,6 +434,17 @@ static void blkg_destroy_all(struct request_queue *q) spin_lock(&blkcg->lock); blkg_destroy(blkg); spin_unlock(&blkcg->lock); + + /* + * in order to avoid holding the spin lock for too long, release + * it when a batch of blkgs are destroyed. + */ + if (!(--count)) { + count = BLKG_BATCH_OP_NUM; + spin_unlock_irq(&q->queue_lock); + cond_resched(); + goto restart; + } }
This part looks good otherwise. Thanks. -- tejun