Commit cf218ddb authored Aug 20, 2020 by Can Guo

block: Fix a race in the runtime power management code



With the current implementation the following race can happen:
* blk_pre_runtime_suspend() calls blk_freeze_queue_start() and
  blk_mq_unfreeze_queue().
* blk_queue_enter() calls blk_queue_pm_only() and that function returns
  true.
* blk_queue_enter() calls blk_pm_request_resume() and that function does
  not call pm_request_resume() because the queue runtime status is
  RPM_ACTIVE.
* blk_pre_runtime_suspend() changes the queue status into RPM_SUSPENDING.

Fix this race by changing the queue runtime status into RPM_SUSPENDING
before switching q_usage_counter to atomic mode.

Change-Id: I5a2c842b959b8c57730b12e4f372abc515a8c8ab
Signed-off-by: Can Guo <cang@codeaurora.org>

parent 67629947

block/blk-pm.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -67,6 +67,10 @@ int blk_pre_runtime_suspend(struct request_queue *q)

		WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE);

		spin_lock_irq(&q->queue_lock);
		q->rpm_status = RPM_SUSPENDING;
		spin_unlock_irq(&q->queue_lock);

		/*
		* Increase the pm_only counter before checking whether any
		* non-PM blk_queue_enter() calls are in progress to avoid that any
		@@ -89,15 +93,13 @@ int blk_pre_runtime_suspend(struct request_queue *q)
		/* Switch q_usage_counter back to per-cpu mode. */
		blk_mq_unfreeze_queue(q);

		if (ret < 0) {
		spin_lock_irq(&q->queue_lock);
		if (ret < 0)
		q->rpm_status = RPM_ACTIVE;
		pm_runtime_mark_last_busy(q->dev);
		else
		q->rpm_status = RPM_SUSPENDING;
		spin_unlock_irq(&q->queue_lock);

		if (ret)
		blk_clear_pm_only(q);
		}

		return ret;
		}