xe_exec_queue_kill() walks the multi-GT list with its own cursor as the
list head:
struct xe_exec_queue *eq = q, *next;
list_for_each_entry_safe(eq, next, &eq->multi_gt_list,
multi_gt_link) {
The head expression is re-evaluated on every loop condition, and by then
eq is the cursor rather than q. multi_gt_list and multi_gt_link are two
names for the same member:
union {
struct list_head multi_gt_list;
struct list_head multi_gt_link;
};
so list_entry_is_head() compares &eq->multi_gt_link with
&eq->multi_gt_list, which is the same address, and the loop stops before
its first iteration. Modelling the layout and the list macros in a small
program shows it plainly:
head = &eq->multi_gt_list : 0 secondary queue(s) visited
head = &q->multi_gt_list : 2 secondary queue(s) visited
For a VM bind queue on a multi-tile device, xe_exec_queue_create_ioctl()
creates one queue per tile and links the others behind the first, so the
loop is what is meant to stop them. Nothing else does: the two calls
after the loop only cover the primary. The secondaries are still freed,
because __xe_exec_queue_free() walks the same list with &q->multi_gt_list
and drops their references, so they go away without q->ops->kill() ever
running and without being removed from the VM with
xe_vm_remove_compute_exec_queue().
Use the primary as the head, the way the other two walks of this list in
the driver already do, in __xe_exec_queue_free() and in
xe_sync_entry_add_deps().
Single tile devices are unaffected, the list is empty there.
I have no multi-tile device, so this is from reading the code and the
program above rather than measured on hardware.
Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: [email protected]
Signed-off-by: Ali Ahmet Memis <[email protected]>
---
The program the commit message refers to, in case it is useful. It uses
the same union layout and the list macros from include/linux/list.h:
struct xe_exec_queue {
int id;
union {
struct list_head multi_gt_list;
struct list_head multi_gt_link;
};
};
eq = &prim;
list_for_each_entry_safe(eq, next, &eq->multi_gt_list, multi_gt_link)
n++; /* n == 0 */
list_for_each_entry_safe(eq, next, &prim.multi_gt_list, multi_gt_link)
n++; /* n == 2 */
Compile tested only, I have no Xe device.
---
drivers/gpu/drm/xe/xe_exec_queue.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c
b/drivers/gpu/drm/xe/xe_exec_queue.c
index 1b5ca3ce578a..85a167857159 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue.c
+++ b/drivers/gpu/drm/xe/xe_exec_queue.c
@@ -1571,9 +1571,9 @@ void xe_exec_queue_update_run_ticks(struct xe_exec_queue
*q)
*/
void xe_exec_queue_kill(struct xe_exec_queue *q)
{
- struct xe_exec_queue *eq = q, *next;
+ struct xe_exec_queue *eq, *next;
- list_for_each_entry_safe(eq, next, &eq->multi_gt_list,
+ list_for_each_entry_safe(eq, next, &q->multi_gt_list,
multi_gt_link) {
q->ops->kill(eq);
xe_vm_remove_compute_exec_queue(q->vm, eq);
base-commit: 0d839570765118029aa8bf4a95444c6a11aacf85
--
2.55.0
