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

From: Andrey Grodzovsky
Date: Tue Apr 24 2018 - 17:02:54 EST

On 04/24/2018 03:44 PM, Daniel Vetter wrote:
On Tue, Apr 24, 2018 at 05:46:52PM +0200, Michel DÃnzer 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@xxxxxxx>
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,
* 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

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;
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)


I think this should be fixed in core code, not papered over in some

Earthling Michel DÃnzer |
Libre software enthusiast | Mesa and X developer
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