lkml.org 
[lkml]   [2018]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process.
    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 <andrey.grodzovsky@amd.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)

    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

    \
     
     \ /
      Last update: 2018-04-24 23:41    [W:4.154 / U:0.072 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site