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.
