[PATCH v2 1/9] block: Fix a race in the runtime power management code

Bart Van Assche
2020-11-16T03:05:30Z

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.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Stanley Chu <stanley.chu@mediatek.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: stable <stable@vger.kernel.org>
Fixes: 986d413b7c15 ("blk-mq: Enable support for runtime power management")
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
block/blk-pm.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/block/blk-pm.c b/block/blk-pm.c
index b85234d758f7..17bd020268d4 100644
--- a/block/blk-pm.c
+++ b/block/blk-pm.c
@@ -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 +93,14 @@ int blk_pre_runtime_suspend(struct request_queue *q)
/* Switch q_usage_counter back to per-cpu mode. */
blk_mq_unfreeze_queue(q);

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

- if (ret)
blk_clear_pm_only(q);
+ }

return ret;
}