On 10/09/2013 04:32 PM, sthu...@codeaurora.org wrote:
>> Hi Aaron,
>>
>> I found a race condition with the block layer runtime PM due to which
>> the q->nr_pending is decremented to less than zero (0xFFFF_FFFF (-1))
>> and hence the blk pre-runtime suspend always returns -EBUSY.
>>
>>
>> The issue is easily reproduced with a scsi disk with disabled tagged
>> command queuing
>>
>> 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
>>
>> Do you have any suggestions on how to fix this issue?
Thanks for the report. I wonder if the following patch helps?
Do the runtime init related work before add_disk, so that every request
is counted properly.
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);
}
Thanks,
Aaron
>>
>>
>> --
>> Regards,
>> Sujit
>>
>
>
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