[Intel-gfx] [PATCH 2/2] drm/i915: Initialise userptr mmu_notifier serial to 1

[Chris Wilson]

During the range invalidate, we walk the list of buffers associated with
the mmu_notifer and find the ones that overlap the range. An
optimisation is made to speed up the iteration by assuming the previous
iter is still valid whilst the tree is unmodified. This exposes a bug
when a range invalidate is triggered after we have just created the
mmu_notifier, but before attaching any buffers. In that case, we presume
we have an unmodified list and start walking from the last iter which is
NULL. Oops.

The easiest fix is then to initialise the serial of the tree to 1.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 7c38f50014db..8e9e91029aed 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -197,7 +197,7 @@ i915_mmu_notifier_get(struct drm_device *dev, struct mm_struct *mm)
 	mmu->mm = mm;
 	mmu->objects = RB_ROOT;
 	mmu->count = 0;
-	mmu->serial = 0;
+	mmu->serial = 1;
 	INIT_LIST_HEAD(&mmu->linear);
 	mmu->is_linear = false;
 
-- 
2.0.1