Messages in this thread | | | Subject | Re: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs | From | Baolin Wang <> | Date | Thu, 28 Jan 2021 11:49:29 +0800 |
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在 2021/1/28 11:41, Jens Axboe 写道: > On 1/27/21 8:22 PM, Baolin Wang wrote: >> On !PREEMPT kernel, we can get below softlockup when doing stress >> testing with creating and destroying block cgroup repeatly. The >> reason is it may take a long time to acquire the queue's lock in >> the loop of blkcg_destroy_blkgs(), or the system can accumulate a >> huge number of blkgs in pathological cases. We can add a need_resched() >> check on each loop and release locks and do cond_resched() if true >> to avoid this issue, since the blkcg_destroy_blkgs() is not called >> from atomic contexts. >> >> [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s! >> [ 4757.010698] Call trace: >> [ 4757.010700] blkcg_destroy_blkgs+0x68/0x150 >> [ 4757.010701] cgwb_release_workfn+0x104/0x158 >> [ 4757.010702] process_one_work+0x1bc/0x3f0 >> [ 4757.010704] worker_thread+0x164/0x468 >> [ 4757.010705] kthread+0x108/0x138 > > Kind of ugly with the two clauses for dropping the blkcg lock, one > being a cpu_relax() and the other a resched. How about something > like this: > > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index 031114d454a6..4221a1539391 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -1016,6 +1016,8 @@ static void blkcg_css_offline(struct cgroup_subsys_state *css) > */ > void blkcg_destroy_blkgs(struct blkcg *blkcg) > { > + might_sleep(); > + > spin_lock_irq(&blkcg->lock); > > while (!hlist_empty(&blkcg->blkg_list)) { > @@ -1023,14 +1025,20 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) > struct blkcg_gq, blkcg_node); > struct request_queue *q = blkg->q; > > - if (spin_trylock(&q->queue_lock)) { > - blkg_destroy(blkg); > - spin_unlock(&q->queue_lock); > - } else { > + if (need_resched() || !spin_trylock(&q->queue_lock)) { > + /* > + * Given that the system can accumulate a huge number > + * of blkgs in pathological cases, check to see if we > + * need to rescheduling to avoid softlockup. > + */ > spin_unlock_irq(&blkcg->lock); > - cpu_relax(); > + cond_resched(); > spin_lock_irq(&blkcg->lock); > + continue; > } > + > + blkg_destroy(blkg); > + spin_unlock(&q->queue_lock); > } > > spin_unlock_irq(&blkcg->lock); >
Looks better to me. Do I need resend with your suggestion? Thanks.
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