From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751155AbeDXVkc (ORCPT ); Tue, 24 Apr 2018 17:40:32 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36920 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750826AbeDXVkb (ORCPT ); Tue, 24 Apr 2018 17:40:31 -0400 X-Google-Smtp-Source: AIpwx49q3d08+sunu8x3aBIFs0oczWDIX6h/wtqfzeXU5yYl8/dGIECs6PIJ1AJbgppVncIAmCQRvg== Date: Tue, 24 Apr 2018 23:40:27 +0200 From: Daniel Vetter To: Andrey Grodzovsky Cc: Michel =?iso-8859-1?Q?D=E4nzer?= , linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, David.Panariti@amd.com, oleg@redhat.com, ebiederm@xmission.com, Alexander.Deucher@amd.com, akpm@linux-foundation.org, Christian.Koenig@amd.com Subject: Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process. Message-ID: <20180424214027.GG25142@phenom.ffwll.local> Mail-Followup-To: Andrey Grodzovsky , Michel =?iso-8859-1?Q?D=E4nzer?= , linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, David.Panariti@amd.com, oleg@redhat.com, ebiederm@xmission.com, Alexander.Deucher@amd.com, akpm@linux-foundation.org, Christian.Koenig@amd.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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 4.15.0-1-amd64 User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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, > 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. -Daniel > > 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@lists.freedesktop.org > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch