Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process.
From: Andrey Grodzovsky
Date: Wed Apr 25 2018 - 09:44:01 EST
On 04/24/2018 05:40 PM, Daniel Vetter wrote:
On Tue, Apr 24, 2018 at 05:02:40PM -0400, Andrey Grodzovsky wrote:
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,
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)
wait_event_killabel doesn't check for fatal_signal_pending before calling
schedule, so definitely has a nice race there.
But if you're sure that you really need to check PF_SIGNALED, then I'm
honestly not clear on what you're trying to pull off here. Your sparse
explanation of what happens isn't enough, since I have no idea how you can
get from get_signal() to the above wait_event_killable callsite.
Fatal signal will trigger process termination during which all FDs are
released, including DRM's.
See here -
[<0>] drm_sched_entity_fini+0x10a/0x3a0 [gpu_sched]
[<0>] amdgpu_ctx_do_release+0x129/0x170 [amdgpu]
[<0>] amdgpu_ctx_mgr_fini+0xd5/0xe0 [amdgpu]
[<0>] amdgpu_driver_postclose_kms+0xcd/0x440 [amdgpu]
[<0>] drm_release+0x414/0x5b0 [drm]
[<0>] __fput+0x176/0x350
[<0>] task_work_run+0xa1/0xc0
(From Eric's explanation above is triggered by do_exit->exit_files)
...
[<0>] do_exit+0x48f/0x1280
[<0>] do_group_exit+0x89/0x140
[<0>] get_signal+0x375/0x8f0
[<0>] do_signal+0x79/0xaa0
[<0>] exit_to_usermode_loop+0x83/0xd0
[<0>] do_syscall_64+0x244/0x270
[<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
Andrey
-Daniel
Andrey
I think this should be fixed in core code, not papered over in some
subsystem.
-Daniel
--
Earthling Michel DÃnzer | http://www.amd.com
Libre software enthusiast | Mesa and X developer
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