On Wed, Sep 19, 2018 at 02:39:35PM -0700, Bart Van Assche wrote: > On Wed, 2018-09-19 at 12:05 +0800, Ming Lei wrote: > > Looks this patch may introduce the following race between queue > > freeze and > > runtime suspend: > > > > ------------------------------------------------------------------- > > ------- > > CPU0 CPU1 > > CPU2 > > ------------------------------------------------------------------- > > ------- > > > > blk_freeze_queue() > > > > blk_mq_alloc_request() > > blk_queue_enter() > > blk_pm_request_ > > resume() > > wait_event() > > > > > > blk_pre_runtime_suspend() > > > > ->blk_set_pm_only > > > > ... > > > > blk_post_runtime_suspend() > > > > ... > > blk_mq_unfreeze_queue() > > ------------------------------------------------------------------- > > ------- > > - CPU0: queue is frozen > > > > - CPU1: one new request comes, and see queue is frozen, but queue > > isn't > > runtime-suspended yet, then blk_pm_request_resume() does nothing. So > > this > > allocation is blocked in wait_event(). > > > > - CPU2: runtime suspend comes, and queue becomes runtime-suspended > > now > > > > - CPU0: queue is unfreeze, but the new request allocation in CPU1 may > > never > > be done because the queue is runtime suspended, and wait_event() > > won't return. > > And the expected result is that the queue becomes active and the > > allocation on > > CPU1 is done immediately. > > Hello Ming, > > Just like for the scenario Jianchao reported, I will address this by > only allowing the suspend to proceed if q_usage_counter == 0. Hi Bart, But .q_usage_counter has been zero already in the case I described, no one grabs a queue ref before starting runtime suspend. Also, if there is in-progress PM request, the .q_usage_counter can be non-zero, but it should be fine to start the suspend. Thanks, Ming
