[SCSI] sd: call blk_pm_runtime_init before add_disk

Sujit has found a race condition that would make q->nr_pending
unbalanced, it occurs as Sujit explained:

"
sd_probe_async() ->
	add_disk() ->
		disk_add_event() ->
			schedule(disk_events_workfn)
	sd_revalidate_disk()
	blk_pm_runtime_init()
return;

Let's say the disk_events_workfn() calls sd_check_events() which tries
to send test_unit_ready() and because of sd_revalidate_disk() trying to
send another commands the test_unit_ready() might be re-queued as the
tagged command queuing is disabled.

So the race condition is -

Thread 1 			  |		Thread 2
sd_revalidate_disk()		  |	sd_check_events()
...nr_pending = 0 as q->dev = NULL|	scsi_queue_insert()
blk_runtime_pm_init()		  | 	blk_pm_requeue_request() ->
				  |	nr_pending = -1 since
				  |	q->dev != NULL
"

The problem is, the test_unit_ready request doesn't get counted the
first time it is queued, so the later decrement of q->nr_pending in
blk_pm_requeue_request makes it unbalanced.

Fix this by calling blk_pm_runtime_init before add_disk so that all
requests initiated there will all be counted.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Reported-and-tested-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index e62d17d41d4e7b84ddf7469194aa0c63d541d59d..5693f6d7eddb8b20cd9b3e0374a4e73e60ab7aa2 100644 (file)
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2854,6 +2854,7 @@ static void sd_probe_async(void *data, async_cookie_t cookie)
                gd->events |= DISK_EVENT_MEDIA_CHANGE;
        }
 
+       blk_pm_runtime_init(sdp->request_queue, dev);
        add_disk(gd);
        if (sdkp->capacity)
                sd_dif_config_host(sdkp);
@@ -2862,7 +2863,6 @@ static void sd_probe_async(void *data, async_cookie_t cookie)
 
        sd_printk(KERN_NOTICE, sdkp, "Attached SCSI %sdisk\n",
                  sdp->removable ? "removable " : "");
-       blk_pm_runtime_init(sdp->request_queue, dev);
        scsi_autopm_put_device(sdp);
        put_device(&sdkp->dev);
 }