Re: kernel BUG scsi_dh_alua sleeping from invalid context && kernel WARNING do not call blocking ops when !TASK_RUNNING

[Martin Wilck <mwilck@suse.com>]

On Tue, 2023-01-17 at 13:52 -0800, Bart Van Assche wrote:
> On 1/17/23 13:48, Martin Wilck wrote:
> > Yes, that was my suggestion. Just defer the scsi_device_put() call
> > in
> > alua_rtpg_queue() in the case where the actual RTPG handler is not
> > queued. I won't have time for that before next week though.
> 
> Hi Martin,
> 
> Do you agree that the call trace shared by Steffen is not sufficient
> to 
> conclude that this change is necessary?

Hmm, I suppose I missed your point... to re-iterate my thinking:

 1 alua_queue_rtpg() must take a ref to the sdev before queueing work,
   whether or not the caller already has one
 2 queue_delayed_work() can fail
 3 if queue_delayed_work() fails, alua_queue_rtpg() must drop the ref
   it just took
 4 BUT (and this is what I guess I missed) this ref can't be the last
   one dropped, because the caller of alua_rtpg_queue() must still hold
   a reference. And scsi_device_put() only sleeps if the last ref is
   dropped. Therefore the issue in Steffen's call stack should
   indeed be fixed just by removing the might_sleep(). If all callers
   callers of alua_rtpg_queue() must hold an sdev reference (I believe 
   they do), we can indeed remove the might_sleep() entirely.

Is this correct reasoning, and what you meant previously? If yes, I
agree, and I apologize for not realizing it in the first place. 
But I think this is subtle enough to deserve a comment in the code.

Thanks
Martin