> On 10/09/2013 04:32 PM, sthumma@xxxxxxxxxxxxxx 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? Thanks it works. Would you like to send formal patch for this? You can add my tested-by ack. Tested-by: Sujit Reddy Thumma <sthumma@xxxxxxxxxxxxxx> > > 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 >>> >> >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
