[PATCH] drm: Require __GFP_NOFAIL for the legacy drm_modeset_lock_all

[Chris Wilson]

Quoting Daniel Vetter (2017-10-31 16:38:26)
> On Tue, Oct 31, 2017 at 03:28:01PM +0200, Ville Syrjälä wrote:
> > On Tue, Oct 31, 2017 at 11:55:35AM +0000, Chris Wilson wrote:
> > > To acquire all modeset locks requires a ww_ctx to be allocated. As this
> > > is the legacy path and the allocation small, to reduce the changes
> > > required (and complex untested error handling) to the legacy drivers, we
> > > simply assume that the allocation succeeds. At present, it relies on the
> > > too-small-to-fail rule, but syzbot found that by injecting a failure
> > > here we would hit the WARN. Document that this allocation must succeed
> > > with __GFP_NOFAIL.
> 
> Note that for atomic drivers at least all the core/helper paths are fixed
> up correctly. But e.g. i915 has still plenty of callsites in its own code,
> mostly debugfs.
> 
> > > Reported-by: syzbot (syzkaller)
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > 
> > Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Applied, thanks.

Just curious as it hasn't shown up in drm-tip yet, so I'm worrying if it
found a crack to hide in.
-Chris