On 9/24/18 7:11 PM, jianchao.wang wrote:
Hi Keith
On 09/25/2018 05:09 AM, Keith Busch wrote:
- /* A deadlock might occur if a request is stuck requiring a
- * timeout at the same time a queue freeze is waiting
- * completion, since the timeout code would not be able to
- * acquire the queue reference here.
- *
- * That's why we don't use blk_queue_enter here; instead, we use
- * percpu_ref_tryget directly, because we need to be able to
- * obtain a reference even in the short window between the queue
- * starting to freeze, by dropping the first reference in
- * blk_freeze_queue_start, and the moment the last request is
- * consumed, marked by the instant q_usage_counter reaches
- * zero.
- */
- if (!percpu_ref_tryget(&q->q_usage_counter))
+ if (!blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next))
return;
We cannot discard the percpu_ref_tryget here.
There following code in blk_mq_timeout_work still need it:
if (next != 0) {
mod_timer(&q->timeout, next);
} else {
queue_for_each_hw_ctx(q, hctx, i) {
/* the hctx may be unmapped, so check it here */
if (blk_mq_hw_queue_mapped(hctx))
blk_mq_tag_idle(hctx);
}
}
Hi Jianchao,
Had you noticed that the percpu_ref_tryget() call has been moved into
blk_mq_queue_tag_busy_iter()?
Bart.
