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drm: Require __GFP_NOFAIL for the legacy drm_modeset_lock_all 

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.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171031115535.15166-1-chris@chris-wilson.co.uk
hifive-unleashed-5.1
Chris Wilson 2017-10-31 11:55:35 +00:00 committed by Daniel Vetter
parent 62884cd386
commit d18d1a5ac8
1 changed files with 1 additions and 1 deletions
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drivers/gpu/drm/drm_modeset_lock.c
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@ -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;