linux-kernel - Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process.

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Message-ID: <aa2d8587-651e-2c24-a673-4682e7035a8f@amd.com>
Date:   Tue, 24 Apr 2018 17:02:40 -0400
From:   Andrey Grodzovsky <Andrey.Grodzovsky@....com>
To:     Michel Dänzer <michel@...nzer.net>,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, David.Panariti@....com,
        oleg@...hat.com, ebiederm@...ssion.com, Alexander.Deucher@....com,
        akpm@...ux-foundation.org, Christian.Koenig@....com
Subject: Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for
 signaled process.

On 04/24/2018 03:44 PM, Daniel Vetter wrote:
> On Tue, Apr 24, 2018 at 05:46:52PM +0200, Michel Dänzer wrote:
>> Adding the dri-devel list, since this is driver independent code.
>>
>>
>> On 2018-04-24 05:30 PM, Andrey Grodzovsky wrote:
>>> Avoid calling wait_event_killable when you are possibly being called
>>> from get_signal routine since in that case you end up in a deadlock
>>> where you are alreay blocked in singla processing any trying to wait
>> Multiple typos here, "[...] already blocked in signal processing and [...]"?
>>
>>
>>> on a new signal.
>>>
>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@....com>
>>> ---
>>>   drivers/gpu/drm/scheduler/gpu_scheduler.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> index 088ff2b..09fd258 100644
>>> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> @@ -227,9 +227,10 @@ void drm_sched_entity_do_release(struct drm_gpu_scheduler *sched,
>>>   		return;
>>>   	/**
>>>   	 * The client will not queue more IBs during this fini, consume existing
>>> -	 * queued IBs or discard them on SIGKILL
>>> +	 * queued IBs or discard them when in death signal state since
>>> +	 * wait_event_killable can't receive signals in that state.
>>>   	*/
>>> -	if ((current->flags & PF_SIGNALED) && current->exit_code == SIGKILL)
>>> +	if (current->flags & PF_SIGNALED)
> You want fatal_signal_pending() here, instead of inventing your own broken
> version.

I rely on current->flags & PF_SIGNALED because this being set from 
within get_signal,
meaning I am within signal processing  in which case I want to avoid any 
signal based wait for that task,
 From what i see in the code, task_struct.pending.signal is being set 
for other threads in same
group (zap_other_threads) or for other scenarios, those task are still 
able to receive signals
so calling wait_event_killable there will not have problem.
>>>   		entity->fini_status = -ERESTARTSYS;
>>>   	else
>>>   		entity->fini_status = wait_event_killable(sched->job_scheduled,
> But really this smells like a bug in wait_event_killable, since
> wait_event_interruptible does not suffer from the same bug. It will return
> immediately when there's a signal pending.

Even when wait_event_interruptible is called as following - 
...->do_signal->get_signal->....->wait_event_interruptible ?
I haven't tried it but wait_event_interruptible is very much alike to 
wait_event_killable so I would assume it will also
not be interrupted if called like that. (Will give it a try just out of 
curiosity anyway)

Andrey

>
> I think this should be fixed in core code, not papered over in some
> subsystem.
> -Daniel
>
>>
>> -- 
>> Earthling Michel Dänzer               |               http://www.amd.com
>> Libre software enthusiast             |             Mesa and X developer
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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