[PATCH 3.11 32/94] SCSI: sd: call blk_pm_runtime_init before add_disk

From: Greg Kroah-Hartman
Date: Sat Nov 09 2013 - 02:16:31 EST


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

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

From: Aaron Lu <aaron.lu@xxxxxxxxx>

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@xxxxxxxxx>
Reported-and-tested-by: Sujit Reddy Thumma <sthumma@xxxxxxxxxxxxxx>
Signed-off-by: James Bottomley <JBottomley@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2853,6 +2853,7 @@ 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);
@@ -2861,7 +2862,6 @@ 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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