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Message-ID: <ac039a7e-4152-4df5-af3d-c952cedfa6dd@stanley.mountain>
Date: Wed, 30 Apr 2025 12:49:13 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: "Sharma, Shashank" <Shashank.Sharma@....com>
Cc: "Deucher, Alexander" <Alexander.Deucher@....com>,
"Koenig, Christian" <Christian.Koenig@....com>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
"Khatri, Sunil" <Sunil.Khatri@....com>,
"Yadav, Arvind" <Arvind.Yadav@....com>,
"Paneer Selvam, Arunpravin" <Arunpravin.PaneerSelvam@....com>,
"amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] drm/amdgpu/userq: remove unnecessary NULL check
On Wed, Apr 30, 2025 at 09:28:59AM +0000, Sharma, Shashank wrote:
> [AMD Official Use Only - AMD Internal Distribution Only]
>
> Hello Dan,
>
> ________________________________
> From: Dan Carpenter
> Sent: Wednesday, April 30, 2025 10:05 AM
> To: Deucher, Alexander
> Cc: Koenig, Christian; David Airlie; Simona Vetter; Sharma, Shashank; Khatri, Sunil; Yadav, Arvind; Paneer Selvam, Arunpravin; amd-gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org; kernel-janitors@...r.kernel.org
> Subject: [PATCH] drm/amdgpu/userq: remove unnecessary NULL check
>
> The "ticket" pointer points to in the middle of the &exec struct so it
> can't be NULL. Remove the check.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> index b0e8098a3988..7505d920fb3d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> @@ -631,7 +631,7 @@ amdgpu_userq_validate_bos(struct amdgpu_userq_mgr *uq_mgr)
> clear = false;
> unlock = true;
> /* The caller is already holding the reservation lock */
> - } else if (ticket && dma_resv_locking_ctx(resv) == ticket) {
> + } else if (dma_resv_locking_ctx(resv) == ticket) {
>
> Its a Nack for me, There are a few situations (particularly during the
> first launch of the desktop, and also when eviction fence and new queue
> creation are working in parallel) where this ticket can be NULL, we
> observed it during the stress validation and hence added this check,
>
It shouldn't be NULL. It sounds like you are experiencing stack
corruption and this is just a bandaid.
drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
566 static int
567 amdgpu_userq_validate_bos(struct amdgpu_userq_mgr *uq_mgr)
568 {
569 struct amdgpu_fpriv *fpriv = uq_mgr_to_fpriv(uq_mgr);
570 struct amdgpu_vm *vm = &fpriv->vm;
571 struct amdgpu_device *adev = uq_mgr->adev;
572 struct amdgpu_bo_va *bo_va;
573 struct ww_acquire_ctx *ticket;
574 struct drm_exec exec;
^^^^^^^^^^^^^^^^^^^^^
The "exec" struct is declared on the stack.
575 struct amdgpu_bo *bo;
576 struct dma_resv *resv;
577 bool clear, unlock;
578 int ret = 0;
579
580 drm_exec_init(&exec, DRM_EXEC_IGNORE_DUPLICATES, 0);
581 drm_exec_until_all_locked(&exec) {
582 ret = amdgpu_vm_lock_pd(vm, &exec, 2);
583 drm_exec_retry_on_contention(&exec);
584 if (unlikely(ret)) {
585 DRM_ERROR("Failed to lock PD\n");
586 goto unlock_all;
587 }
588
589 /* Lock the done list */
590 list_for_each_entry(bo_va, &vm->done, base.vm_status) {
591 bo = bo_va->base.bo;
592 if (!bo)
593 continue;
594
595 ret = drm_exec_lock_obj(&exec, &bo->tbo.base);
596 drm_exec_retry_on_contention(&exec);
597 if (unlikely(ret))
598 goto unlock_all;
599 }
600 }
601
602 spin_lock(&vm->status_lock);
603 while (!list_empty(&vm->moved)) {
604 bo_va = list_first_entry(&vm->moved, struct amdgpu_bo_va,
605 base.vm_status);
606 spin_unlock(&vm->status_lock);
607
608 /* Per VM BOs never need to bo cleared in the page tables */
609 ret = amdgpu_vm_bo_update(adev, bo_va, false);
610 if (ret)
611 goto unlock_all;
612 spin_lock(&vm->status_lock);
613 }
614
615 ticket = &exec.ticket;
^^^^^^^^^^^^^^^^^^^^^
ticket is only set here. We know that &exec is non-NULL because it's
declared on the stack. ticket is 4 bytes into the middle of a non-NULL
struct. It is impossible for ticket to be NULL here.
616 while (!list_empty(&vm->invalidated)) {
617 bo_va = list_first_entry(&vm->invalidated, struct amdgpu_bo_va,
618 base.vm_status);
619 resv = bo_va->base.bo->tbo.base.resv;
620 spin_unlock(&vm->status_lock);
621
622 bo = bo_va->base.bo;
623 ret = amdgpu_userq_validate_vm_bo(NULL, bo);
624 if (ret) {
625 DRM_ERROR("Failed to validate BO\n");
626 goto unlock_all;
627 }
628
629 /* Try to reserve the BO to avoid clearing its ptes */
630 if (!adev->debug_vm && dma_resv_trylock(resv)) {
631 clear = false;
632 unlock = true;
633 /* The caller is already holding the reservation lock */
634 } else if (ticket && dma_resv_locking_ctx(resv) == ticket) {
I've included the whole rest of the function so that we can see it is not
set a second time.
regards,
dan carpenter
635 clear = false;
636 unlock = false;
637 /* Somebody else is using the BO right now */
638 } else {
639 clear = true;
640 unlock = false;
641 }
642
643 ret = amdgpu_vm_bo_update(adev, bo_va, clear);
644
645 if (unlock)
646 dma_resv_unlock(resv);
647 if (ret)
648 goto unlock_all;
649
650 spin_lock(&vm->status_lock);
651 }
652 spin_unlock(&vm->status_lock);
653
654 ret = amdgpu_eviction_fence_replace_fence(&fpriv->evf_mgr, &exec);
655 if (ret)
656 DRM_ERROR("Failed to replace eviction fence\n");
657
658 unlock_all:
659 drm_exec_fini(&exec);
660 return ret;
661 }
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