[PATCH] drm: Require __GFP_NOFAIL for the legacy drm_modeset_lock_all

[Daniel Vetter]

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.
-Daniel

> 
> > ---
> > Resent to the right list!
> > ---
> >  drivers/gpu/drm/drm_modeset_lock.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
> > index e123497da0ca..963e23db0fe7 100644
> > --- a/drivers/gpu/drm/drm_modeset_lock.c
> > +++ b/drivers/gpu/drm/drm_modeset_lock.c
> > @@ -93,7 +93,7 @@ void drm_modeset_lock_all(struct drm_device *dev)
> >  	struct drm_modeset_acquire_ctx *ctx;
> >  	int ret;
> >  
> > -	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> > +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
> >  	if (WARN_ON(!ctx))
> >  		return;
> >  
> > -- 
> > 2.15.0.rc2
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Ville Syrjälä
> Intel OTC

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch