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?
--
Regards,
Sujit
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