This is a note to let you know that I've just added the patch titled
SCSI: sd: call blk_pm_runtime_init before add_disk
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
scsi-sd-call-blk_pm_runtime_init-before-add_disk.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 10c580e4239df5c3344ca00322eca86ab2de880b Mon Sep 17 00:00:00 2001
From: Aaron Lu <aaron.lu@xxxxxxxxx>
Date: Thu, 10 Oct 2013 13:22:36 +0800
Subject: SCSI: sd: call blk_pm_runtime_init before add_disk
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
@@ -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);
}
Patches currently in stable-queue which might be from aaron.lu@xxxxxxxxx are
queue-3.10/scsi-sd-call-blk_pm_runtime_init-before-add_disk.patch
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