On 07/29/2016 11:52 AM, Gabriel Krisman Bertazi wrote:
Jens Axboe <axboe@xxxxxxxxx> writes:
I can see that is an issue. Did you consider the case where
blk_mq_timeout_work() is entered, but we don't have any requests
allocated that currently hold a reference? This could happen if
completion races with a timeout.
Hi Jens,
That shouldn't be an issue, I think. The only functional difference
should be during queue freezes, and in this case, if the request was
already completed by the time we touch it, we`ll only hold the queue
freeze for a little longer, until we release the reference by the end of
the timeout path. should the final request be released before
blk_mq_timeout_work acquire it's reference, q_usage_counter will reach
zero, and the call to percpu_ref_tryget will fail the same way
percpu_ref_tryget_live would.
Thanks, I'm happy with it, and the detailed comment is a good
improvement. I have added it for this series.
--
Jens Axboe
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