On 2020-09-14 00:19, Yang Yang wrote:
> There is a race between blk_queue_enter() and block layer's runtime
> suspend.
>
> CPU0 CPU1
> --------------------------------- -------------------------------
> blk_pre_runtime_suspend(q) { blk_queue_enter() {
> /* q->rpm_status=RPM_ACTIVE */
> blk_set_pm_only(q)
> /* q->pm_only=1 */
> blk_freeze_queue_start(q)
> blk_mq_unfreeze_queue(q)
> if (percpu_ref_tryget_live()) {
> /* pm=0 && q->pm_only=1 */
> if (pm || !blk_queue_pm_only(q)) {
> } else {
> percpu_ref_put()
> }
> }
> wait_event(q->mq_freeze_wq,
> (!q->mq_freeze_depth &&
> /* q->rpm_status=RPM_ACTIVE
> q->pm_only=1 */
> (pm || (blk_pm_request_resume(q),
> !blk_queue_pm_only(q)))) ||
> blk_queue_dying(q))
> }
> spin_lock_irq(&q->queue_lock)
> q->rpm_status = RPM_SUSPENDING
> spin_unlock_irq(&q->queue_lock)
> }
>
> At this point blk_pm_request_resume() missed the chance to resume the
> queue, so blk_queue_enter() may wait here forever.
> The solution is to wake up the mq_freeze_wq after runtime suspend
> completed, make blk_pm_request_resume() reexamine the q->rpm_status flag.
>
> Signed-off-by: Yang Yang <yang.yang@xxxxxxxx>
> ---
> block/blk-pm.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/block/blk-pm.c b/block/blk-pm.c
> index b85234d758f7..dec7d0aef606 100644
> --- a/block/blk-pm.c
> +++ b/block/blk-pm.c
> @@ -132,6 +132,8 @@ void blk_post_runtime_suspend(struct request_queue *q, int err)
>
> if (err)
> blk_clear_pm_only(q);
> + else
> + wake_up_all(&q->mq_freeze_wq);
> }
> EXPORT_SYMBOL(blk_post_runtime_suspend);
Please verify whether the following patch series also fixes the reported
hang: https://lore.kernel.org/linux-block/20200906012219.17893-1-bvanassche@xxxxxxx/T/#t
Thanks,
Bart.
