[PATCH] drm/xe: Fix potential NULL deref in xe_exec_queue_tlb_inval_last_fence_put_unlocked

[Shuicheng Lin <shuicheng.lin@intel.com>]

xe_exec_queue_tlb_inval_last_fence_put_unlocked() uses q->vm->xe as the
first argument to xe_assert(). This function is called unconditionally
from xe_exec_queue_destroy() for all queues, including kernel queues
that have q->vm == NULL (e.g., queues created during GT init in
xe_gt_record_default_lrcs() with vm=NULL).

While current compilers optimize away the q->vm->xe dereference (even
in CONFIG_DRM_XE_DEBUG=y builds, the compiler pushes the dereference
into the WARN branch that is only taken when the assert condition is
false), the code is semantically incorrect and constitutes undefined
behavior in the C abstract machine for the NULL pointer case.

Use gt_to_xe(q->gt) instead, which is always valid for any exec queue.
This is consistent with how xe_exec_queue_destroy() itself obtains the
xe_device pointer in its own xe_assert at the top of the function.

Fixes: b2d7ec41f2a3 ("drm/xe: Attach last fence to TLB invalidation job queues")
Cc: Matthew Brost <matthew.brost@intel.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
---
 drivers/gpu/drm/xe/xe_exec_queue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
index 4603ff08d860..071b8c41df43 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue.c
+++ b/drivers/gpu/drm/xe/xe_exec_queue.c
@@ -1763,7 +1763,7 @@ void xe_exec_queue_tlb_inval_last_fence_put(struct xe_exec_queue *q,
 void xe_exec_queue_tlb_inval_last_fence_put_unlocked(struct xe_exec_queue *q,
 						     unsigned int type)
 {
-	xe_assert(q->vm->xe, type == XE_EXEC_QUEUE_TLB_INVAL_MEDIA_GT ||
+	xe_assert(gt_to_xe(q->gt), type == XE_EXEC_QUEUE_TLB_INVAL_MEDIA_GT ||
 		  type == XE_EXEC_QUEUE_TLB_INVAL_PRIMARY_GT);
 
 	dma_fence_put(q->tlb_inval[type].last_fence);
-- 
2.43.0