Re: [PATCH V2] SCSI: fix queue cleanup race before queue initialization is done

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On Wed, 2018-11-14 at 16:25 +-0800, Ming Lei wrote:
+AD4 --- a/drivers/scsi/scsi+AF8-lib.c
+AD4 +-+-+- b/drivers/scsi/scsi+AF8-lib.c
+AD4 +AEAAQA -697,6 +-697,12 +AEAAQA static bool scsi+AF8-end+AF8-request(struct request +ACo-req,
+AD4 blk+AF8-status+AF8-t error,
+AD4  		 +ACo-/
+AD4  		scsi+AF8-mq+AF8-uninit+AF8-cmd(cmd)+ADs
+AD4  
+AD4 +-		/+ACo
+AD4 +-		 +ACo queue is still alive, so grab the ref for preventing it
+AD4 +-		 +ACo from being cleaned up during running queue.
+AD4 +-		 +ACo-/
+AD4 +-		percpu+AF8-ref+AF8-get(+ACY-q-+AD4-q+AF8-usage+AF8-counter)+ADs
+AD4 +-

I think the above comment is misleading. In the block layer a queue is called
alive if the +ACI-dying+ACI flag has not been set. When the above call to
percpu+AF8-ref+AF8-get() occurs it is not guaranteed that that flag has not yet been
set. But it is guaranteed that q-+AD4-q+AF8-usage+AF8-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.



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