From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process. Date: Tue, 24 Apr 2018 17:11:44 -0500 Message-ID: <87a7ts2r1b.fsf@xmission.com> References: <1524583836-12130-1-git-send-email-andrey.grodzovsky@amd.com> <1524583836-12130-3-git-send-email-andrey.grodzovsky@amd.com> <7313704c-0693-0bb9-8818-99cd2b7c0ca0@daenzer.net> <20180424194418.GE25142@phenom.ffwll.local> <87tvs05mik.fsf@xmission.com> <27d7d15b-f7c3-2a0a-af85-eb243526ac88@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <27d7d15b-f7c3-2a0a-af85-eb243526ac88@amd.com> (Andrey Grodzovsky's message of "Tue, 24 Apr 2018 17:37:08 -0400") Sender: linux-kernel-owner@vger.kernel.org To: Andrey Grodzovsky Cc: Michel =?utf-8?Q?D=C3=A4nzer?= , linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, David.Panariti@amd.com, oleg@redhat.com, Alexander.Deucher@amd.com, akpm@linux-foundation.org, Christian.Koenig@amd.com List-Id: amd-gfx.lists.freedesktop.org Andrey Grodzovsky writes: > On 04/24/2018 05:21 PM, Eric W. Biederman wrote: >> Andrey Grodzovsky writes: >> >>> 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 >>>>>> --- >>>>>> 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, >> It doesn't mean that. Unless you are called by do_coredump (you >> aren't). > > Looking in latest code here > https://elixir.bootlin.com/linux/v4.17-rc2/source/kernel/signal.c#L2449 > i see that current->flags |= PF_SIGNALED; is out side of > if (sig_kernel_coredump(signr)) {...} scope In small words. You showed me the backtrace and I have read the code. PF_SIGNALED means you got killed by a signal. get_signal do_coredump do_group_exit do_exit exit_signals sets PF_EXITING exit_mm calls fput on mmaps calls sched_task_work exit_files calls fput on open files calls sched_task_work exit_task_work task_work_run /* you are here */ So strictly speaking you are inside of get_signal it is not meaningful to speak of yourself as within get_signal. I am a little surprised to see task_work_run called so early. I was mostly expecting it to happen when the dead task was scheduling away, like normally happens. Testing for PF_SIGNALED does not give you anything at all that testing for PF_EXITING (the flag that signal handling is shutdown) does not get you. There is no point in distinguishing PF_SIGNALED from any other path to do_exit. do_exit never returns. The task is dead. Blocking indefinitely while shutting down a task is a bad idea. Blocking indefinitely while closing a file descriptor is a bad idea. The task has been killed it can't get more dead. SIGKILL is meaningless at this point. So you need a timeout, or not to wait at all. Eric