Re: [PATCH 3/3] drm/amdgpu: Switch to interrupted wait to recover from ring hang.

[Andrey Grodzovsky]

On 04/24/2018 12:30 PM, Eric W. Biederman wrote:
> "Panariti, David" <David.Panariti@xxxxxxx> writes:
>
> > Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx> writes:
> > > Kind of dma_fence_wait_killable, except that we don't have such API
> > > (maybe worth adding ?)
> > Depends on how many places it would be called, or think it might be called.  Can always factor on the 2nd time it's needed.
> > Factoring, IMO, rarely hurts.  The factored function can easily be visited using `M-.' ;->
> >
> > Also, if the wait could be very long, would a log message, something like "xxx has run for Y seconds."  help?
> > I personally hate hanging w/no info.
> Ugh.  This loop appears susceptible to loosing wake ups.  There are
> races between when a wake-up happens, when we clear the sleeping state,
> and when we test the stat to see if we should stat awake.  So yes
> implementing a dma_fence_wait_killable that handles of all that
> correctly sounds like an very good idea.

I am not clear here - could you be more specific about what races will 
happen here, more bellow
> Eric
>
>
> > > If the ring is hanging for some reason allow to recover the waiting by sending fatal signal.
> > >
> > > Originally-by: David Panariti <David.Panariti@xxxxxxx>
> > > Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
> > > ---
> > >    drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 14 ++++++++++----
> > >    1 file changed, 10 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > > index eb80edf..37a36af 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > > @@ -421,10 +421,16 @@ int amdgpu_ctx_wait_prev_fence(struct amdgpu_ctx *ctx, unsigned ring_id)
> > >
> > >        if (other) {
> > >                signed long r;
> > > -             r = dma_fence_wait_timeout(other, false, MAX_SCHEDULE_TIMEOUT);
> > > -             if (r < 0) {
> > > -                     DRM_ERROR("Error (%ld) waiting for fence!\n", r);
> > > -                     return r;
> > > +
> > > +             while (true) {
> > > +                     if ((r = dma_fence_wait_timeout(other, true,
> > > +                                     MAX_SCHEDULE_TIMEOUT)) >= 0)
> > > +                             return 0;
> > > +

Do you mean that by the time I reach here some other thread from my 
group already might dequeued SIGKILL since it's a shared signal and 
hence fatal_signal_pending will return false ? Or are you talking about 
the dma_fence_wait_timeout implementation in dma_fence_default_wait with 
schedule_timeout ?

Andrey

> > > +                     if (fatal_signal_pending(current)) {
> > > +                             DRM_ERROR("Error (%ld) waiting for fence!\n", r);
> > > +                             return r;
> > > +                     }
> > >                }
> > >        }
> > >
> > > --
> > > 2.7.4
> Eric