From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 31 Oct 2017 11:55:35 +0000
Subject: drm: Require __GFP_NOFAIL for the legacy drm_modeset_lock_all
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Git-commit: d18d1a5ac811d12f7ebc1129230312b5f2c50cb8
Patch-mainline: v4.15-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

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

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/drm_modeset_lock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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_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;