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...@intel.com>
Reported-and-tested-by: Sujit Reddy Thumma <sthu...@codeaurora.org>
Cc: sta...@vger.kernel.org
---
drivers/scsi/sd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index e62d17d..5693f6d 100644
--- 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);
}
--
1.8.4.12.g2ea3df6
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