[bug report] drm/xe/pxp: Add PXP queue tracking and session start

[Dan Carpenter]

Hello Daniele Ceraolo Spurio,

Commit f8caa80154c4 ("drm/xe/pxp: Add PXP queue tracking and session
start") from Jan 29, 2025 (linux-next), leads to the following Smatch
static checker warning:

	drivers/gpu/drm/xe/xe_vm.c:286 xe_vm_remove_compute_exec_queue()
	warn: sleeping in atomic context

drivers/gpu/drm/xe/xe_vm.c
    281 void xe_vm_remove_compute_exec_queue(struct xe_vm *vm, struct xe_exec_queue *q)
    282 {
    283         if (!xe_vm_in_preempt_fence_mode(vm))
    284                 return;
    285 
--> 286         down_write(&vm->lock);
    287         if (!list_empty(&q->lr.link)) {
    288                 list_del_init(&q->lr.link);
    289                 --vm->preempt.num_exec_queues;
    290         }
    291         if (q->lr.pfence) {
    292                 dma_fence_enable_sw_signaling(q->lr.pfence);
    293                 dma_fence_put(q->lr.pfence);
    294                 q->lr.pfence = NULL;
    295         }
    296         up_write(&vm->lock);
    297 }

pxp_invalidate_queues() <- disables preempt
-> xe_exec_queue_kill()
   -> xe_vm_remove_compute_exec_queue()

drivers/gpu/drm/xe/xe_pxp.c
   699  static void pxp_invalidate_queues(struct xe_pxp *pxp)
   700  {
   701          struct xe_exec_queue *tmp, *q;
   702  
   703          spin_lock_irq(&pxp->queues.lock);
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

   704  
   705          /*
   706           * Removing a queue from the PXP list requires a put of the RPM ref that
   707           * the queue holds to keep the PXP session alive, which can't be done
   708           * under spinlock. Since it is safe to kill a queue multiple times, we
   709           * can leave the invalid queue in the list for now and postpone the
   710           * removal and associated RPM put to when the queue is destroyed.
   711           */
   712          list_for_each_entry(tmp, &pxp->queues.list, pxp.link) {
   713                  q = xe_exec_queue_get_unless_zero(tmp);
   714  
   715                  if (!q)
   716                          continue;
   717  
   718                  xe_exec_queue_kill(q);

We can't call xe_exec_queue_kill() while holding a spin_lock.

   719                  xe_exec_queue_put(q);
   720          }
   721  
   722          spin_unlock_irq(&pxp->queues.lock);
   723  }

regards,
dan carpenter