[PATCH 1/3] drm/etnaviv: don't trigger OOM killer when page allocation fails

[Lucas Stach]

Am Montag, den 26.06.2017, 07:52 +0200 schrieb Michal Hocko:
> On Tue 20-06-17 11:25:24, Daniel Vetter wrote:
> > On Tue, Jun 20, 2017 at 11:22:06AM +0200, Lucas Stach wrote:
> > > Am Dienstag, den 20.06.2017, 11:06 +0200 schrieb Daniel Vetter:
> > > > On Tue, Jun 06, 2017 at 09:17:06AM +0200, Lucas Stach wrote:
> > > > > GPU buffers can be quite large, so userspace is expected to
> > > > > deal with
> > > > > allocation failure. Don't trigger the OOM killer when page
> > > > > allocation for
> > > > > the GEM objects fails, as this opens an easy possiblity for
> > > > > unprivileged
> > > > > applications to DOS the system,a s the shmem pages are not
> > > > > fully accounted
> > > > > to the allocating process.
> > > > > 
> > > > > Signed-off-by: Lucas Stach <dev at lynxeye.de>
> > > > > ---
> > > > >  drivers/gpu/drm/etnaviv/etnaviv_gem.c | 3 ++-
> > > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > > b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > > index f0efc5d..4c53508 100644
> > > > > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > > @@ -662,7 +662,8 @@ static struct drm_gem_object
> > > > > *__etnaviv_gem_new(struct drm_device *dev,
> > > > >  		 * going to pin these pages.
> > > > >  		 */
> > > > >  		mapping = obj->filp->f_mapping;
> > > > > -		mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
> > > > > +		mapping_set_gfp_mask(mapping, GFP_HIGHUSER |
> > > > > +				     __GFP_NORETRY |
> > > > > __GFP_NOWARN);
> > > > 
> > > > _NORETRY means the mm does try hard at all to free memory.
> > > > We've just done
> > > > this patch in 4.12 and totally regret it, because now gpu tasks
> > > > run out of
> > > > memory with plenty of (gpu) memory available that could be
> > > > reaped.
> > > > 
> > > > There's some discussions going on with Michal Hocko and Chris
> > > > Wilson
> > > > about possible solutions for this without so much hacks.
> > > 
> > > Thanks for the heads up. In contrast to some of the other drivers
> > > Etnaviv hasn't grown a proper shrinker yet, so I still think this
> > > patch
> > > is a step in the right direction for the time being.
> > > Currently with Etnaviv sitting on lots of GPU memory and the MM
> > > trying
> > > hard to free more memory for GPU usage a simple piglit run might
> > > pressure the OOM killer hard enough to bring the system down by
> > > killing
> > > PID 1.
> > 
> > Ah ok, that changes the balance of course. Time to type that
> > shrinker I'd
> > say :-)
> 
> Yeah, shrinker sounds like an absolute must. Anyway, I've posted
> __GFP_RETRY_MAYFAIL patchset [1] so you can use that flag.
> 
> [1] http://lkml.kernel.org/r/20170623085345.11304-1-mhocko@kernel.org

Thanks, I'll switch etnaviv over to use this flag when the patchset
gets applied.

A proper shrinker is on the TODO list, but there are only so much hours
in a day...

Regards,
Lucas