Re: [PATCH V2] SCSI: fix queue cleanup race before queue initialization is done
From: Bart Van Assche <bvanassche@acm.org>
Date: 2018-11-14 15:02:33
Also in:
linux-scsi, stable
On Wed, 2018-11-14 at 16:25 +0800, Ming Lei wrote:
quoted hunk ↗ jump to hunk
--- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c@@ -697,6 +697,12 @@ static bool scsi_end_request(struct request *req,blk_status_t error, */ scsi_mq_uninit_cmd(cmd); + /* + * queue is still alive, so grab the ref for preventing it + * from being cleaned up during running queue. + */ + percpu_ref_get(&q->q_usage_counter); +
I think the above comment is misleading. In the block layer a queue is called alive if the "dying" flag has not been set. When the above call to percpu_ref_get() occurs it is not guaranteed that that flag has not yet been set. But it is guaranteed that q->q_usage_counter is not zero. I would prefer if the comment would be modified. What's not clear to me is why this patch only protects the blk-mq path but not the legacy path. Does the legacy path need similar protection? It also triggers a queue run after having finished a request. Otherwise this patch looks fine to me. Bart.