From: Bart Van Assche <bvanassche@acm.org>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
Hannes Reinecke <hare@suse.com>, Christoph Hellwig <hch@lst.de>,
Thomas Gleixner <tglx@linutronix.de>,
Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH V10 11/11] block: deactivate hctx when the hctx is actually inactive
Date: Sat, 9 May 2020 07:07:55 -0700 [thread overview]
Message-ID: <954b942e-3b06-4be7-9f2f-23f87ff514f0@acm.org> (raw)
In-Reply-To: <20200505020930.1146281-12-ming.lei@redhat.com>
On 2020-05-04 19:09, Ming Lei wrote:
> @@ -1373,28 +1375,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
> int srcu_idx;
>
[ ... ]
> if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
> - cpu_online(hctx->next_cpu)) {
> - printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n",
> - raw_smp_processor_id(),
> - cpumask_empty(hctx->cpumask) ? "inactive": "active");
> - dump_stack();
> + cpumask_next_and(-1, hctx->cpumask, cpu_online_mask) >=
> + nr_cpu_ids) {
> + blk_mq_hctx_deactivate(hctx);
> + return;
> }
The blk_mq_hctx_deactivate() function calls blk_mq_resubmit_rq()
indirectly. From blk_mq_resubmit_rq():
+ /* avoid allocation failure by clearing NOWAIT */
+ nrq = blk_get_request(rq->q, rq->cmd_flags & ~REQ_NOWAIT, flags);
blk_get_request() calls blk_mq_alloc_request(). blk_mq_alloc_request()
calls blk_queue_enter(). blk_queue_enter() waits until a queue is
unfrozen if freezing of a queue has started. As one can see freezing a
queue triggers a queue run:
void blk_freeze_queue_start(struct request_queue *q)
{
mutex_lock(&q->mq_freeze_lock);
if (++q->mq_freeze_depth == 1) {
percpu_ref_kill(&q->q_usage_counter);
mutex_unlock(&q->mq_freeze_lock);
if (queue_is_mq(q))
blk_mq_run_hw_queues(q, false);
} else {
mutex_unlock(&q->mq_freeze_lock);
}
}
Does this mean that if queue freezing happens after hot unplugging
started that a deadlock will occur because the blk_mq_run_hw_queues()
call in blk_freeze_queue_start() will wait forever?
Bart.
next prev parent reply other threads:[~2020-05-09 14:08 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 2:09 [PATCH V10 00/11] blk-mq: improvement CPU hotplug Ming Lei
2020-05-05 2:09 ` [PATCH V10 01/11] block: clone nr_integrity_segments and write_hint in blk_rq_prep_clone Ming Lei
2020-05-05 2:09 ` [PATCH V10 02/11] block: add helper for copying request Ming Lei
2020-05-05 2:09 ` [PATCH V10 03/11] blk-mq: mark blk_mq_get_driver_tag as static Ming Lei
2020-05-05 2:09 ` [PATCH V10 04/11] blk-mq: assign rq->tag in blk_mq_get_driver_tag Ming Lei
2020-05-05 2:09 ` [PATCH V10 05/11] blk-mq: support rq filter callback when iterating rqs Ming Lei
2020-05-08 23:32 ` Bart Van Assche
2020-05-09 0:18 ` Bart Van Assche
2020-05-09 2:05 ` Ming Lei
2020-05-09 3:08 ` Bart Van Assche
2020-05-09 3:52 ` Ming Lei
2020-05-05 2:09 ` [PATCH V10 06/11] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2020-05-05 6:14 ` Hannes Reinecke
2020-05-08 23:26 ` Bart Van Assche
2020-05-09 2:09 ` Ming Lei
2020-05-09 3:11 ` Bart Van Assche
2020-05-09 3:56 ` Ming Lei
2020-05-05 2:09 ` [PATCH V10 07/11] blk-mq: stop to handle IO and drain IO before hctx becomes inactive Ming Lei
2020-05-08 23:39 ` Bart Van Assche
2020-05-09 2:20 ` Ming Lei
2020-05-09 3:24 ` Bart Van Assche
2020-05-09 4:10 ` Ming Lei
2020-05-09 14:18 ` Bart Van Assche
2020-05-11 1:45 ` Ming Lei
2020-05-11 3:20 ` Bart Van Assche
2020-05-11 3:48 ` Ming Lei
2020-05-11 20:56 ` Bart Van Assche
2020-05-12 1:25 ` Ming Lei
2020-05-05 2:09 ` [PATCH V10 08/11] block: add blk_end_flush_machinery Ming Lei
2020-05-05 2:09 ` [PATCH V10 09/11] blk-mq: add blk_mq_hctx_handle_dead_cpu for handling cpu dead Ming Lei
2020-05-05 2:09 ` [PATCH V10 10/11] blk-mq: re-submit IO in case that hctx is inactive Ming Lei
2020-05-05 2:09 ` [PATCH V10 11/11] block: deactivate hctx when the hctx is actually inactive Ming Lei
2020-05-09 14:07 ` Bart Van Assche [this message]
2020-05-11 2:11 ` Ming Lei
2020-05-11 3:30 ` Bart Van Assche
2020-05-11 4:08 ` Ming Lei
2020-05-11 20:52 ` Bart Van Assche
2020-05-12 1:43 ` Ming Lei
2020-05-12 2:08 ` Ming Lei
2020-05-08 21:49 ` [PATCH V10 00/11] blk-mq: improvement CPU hotplug Ming Lei
2020-05-09 3:17 ` Jens Axboe
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