On 04/24/2018 05:21 PM, Eric W. Biederman wrote: > Andrey Grodzovsky <Andrey.Grodzovsky at amd.com> 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 <andrey.grodzovsky at 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, > 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 Andrey > The closing of files does not happen in do_coredump. > Which means you are being called from do_exit. > In fact you are being called after exit_files which closes > the files. The actual __fput processing happens in task_work_run. > >> 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. > Excpet that you are geing called after from do_exit and after exit_files > which is after exit_signal. Which means that PF_EXITING has been set. > Which implies that the kernel signal handling machinery has already > started being torn down. > > Not as much as I would like to happen at that point as we are still > left with some old CLONE_PTHREAD messes in the code that need to be > cleaned up. > > Still given the fact you are task_work_run it is quite possible even > release_task has been run on that task before the f_op->release method > is called. So you simply can not count on signals working. > > Which in practice leaves a timeout for ending your wait. That code can > legitimately be in a context that is neither interruptible nor killable. > >>>>> 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) > As PF_EXITING is set want_signal should fail and the signal state of the > task should not be updatable by signals. > > Eric > >
