[PATCH v3 1/1] scsi: pm: Balance pm_only counter of request queue during system resume

[Can Guo]

During system resume, scsi_resume_device() decreases a request queue's
pm_only counter if the scsi device was quiesced before. But after that,
if the scsi device's RPM status is RPM_SUSPENDED, the pm_only counter is
still held (non-zero). Current scsi resume hook only sets the RPM status
of the scsi device and its request queue to RPM_ACTIVE, but leaves the
pm_only counter unchanged. This may make the request queue's pm_only
counter remain non-zero after resume hook returns, hence those who are
waiting on the mq_freeze_wq would never be woken up. Fix this by calling
blk_post_runtime_resume() if pm_only is non-zero to balance the pm_only
counter which is held by the scsi device's RPM ops.

(struct request_queue)0xFFFFFF815B69E938
	pm_only = (counter = 2),
	rpm_status = 0,
	dev = 0xFFFFFF815B0511A0,

((struct device)0xFFFFFF815B0511A0)).power
	is_suspended = FALSE,
	runtime_status = RPM_ACTIVE,

(struct scsi_device)0xFFFFFF815b051000
	request_queue = 0xFFFFFF815B69E938,
	sdev_state = SDEV_RUNNING,
	quiesced_by = 0x0,

B::v.f_/task_
-000|__switch_to
-001|context_switch
-001|__schedule
-002|schedule
-003|blk_queue_enter(q = 0xFFFFFF815B69E938, flags = 0)
-004|generic_make_request
-005|submit_bio

Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx>
---

Change since v2:
- Rebased on 5.8-scsi-queue

Change since v1:
- Added more debugging context info

 drivers/scsi/scsi_pm.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 3717eea..4804029 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -93,8 +93,10 @@ static int scsi_dev_type_resume(struct device *dev,
 		 */
 		if (!err && scsi_is_sdev_device(dev)) {
 			struct scsi_device *sdev = to_scsi_device(dev);
-
-			blk_set_runtime_active(sdev->request_queue);
+			if (blk_queue_pm_only(sdev->request_queue))
+				blk_post_runtime_resume(sdev->request_queue, 0);
+			else
+				blk_set_runtime_active(sdev->request_queue);
 		}
 	}
 
-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.