linux-kernel - [PATCH 3.10 24/74] SCSI: sd: call blk_pm_runtime_init before add

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Date:	Fri,  8 Nov 2013 22:51:29 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Aaron Lu <aaron.lu@...el.com>,
	James Bottomley <JBottomley@...allels.com>
Subject: [PATCH 3.10 24/74] SCSI: sd: call blk_pm_runtime_init before add_disk

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aaron Lu <aaron.lu@...el.com>

commit 10c580e4239df5c3344ca00322eca86ab2de880b upstream.

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@...el.com>
Reported-and-tested-by: Sujit Reddy Thumma <sthumma@...eaurora.org>
Signed-off-by: James Bottomley <JBottomley@...allels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/scsi/sd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2843,6 +2843,7 @@ static void sd_probe_async(void *data, a
 		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);
@@ -2851,7 +2852,6 @@ static void sd_probe_async(void *data, a
 
 	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);
 }


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