Re: [PATCH v4] blk-mq: Fix race conditions in request timeout handling

Hello, Ming.

On Tue, Apr 10, 2018 at 11:25:54PM +0800, Ming Lei wrote:

• if (time_after_eq(jiffies, deadline) &&

•   blk_mq_change_rq_state(rq, MQ_RQ_IN_FLIGHT, MQ_RQ_COMPLETE)) {
  

•   blk_mq_rq_timed_out(rq, reserved);
  
  

Normal completion still can happen between blk_mq_change_rq_state() and blk_mq_rq_timed_out().

In tj's approach, there is synchronize_rcu() between writing aborted_gstate and blk_mq_rq_timed_out, it is easier for normal completion to happen during the big window.

I don't think plugging this hole is all that difficult, but this shouldn't lead to any critical failures. If so, that'd be a driver bug.

Thanks.