Re: [PATCH 3/3] drm/ttm: remove ttm_bo_wait_unreserved

From: "Koenig, Christian" <Christian.Koenig@amd.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Hellstrom <thellstrom@vmware.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	"Huang, Ray" <Ray.Huang@amd.com>,
	VMware Graphics <linux-graphics-maintainer@vmware.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 3/3] drm/ttm: remove ttm_bo_wait_unreserved
Date: Tue, 20 Aug 2019 15:34:02 +0000	[thread overview]
Message-ID: <be8f3cda-6788-d424-0135-cb232432fad7@amd.com> (raw)
In-Reply-To: <CAKMK7uEgdViPJgs4Y32DwrC8-yGpPU+G=zq-T9tgnQeVOkG6mg@mail.gmail.com>

Am 20.08.19 um 17:21 schrieb Daniel Vetter:
> On Tue, Aug 20, 2019 at 5:16 PM Koenig, Christian
> <Christian.Koenig@amd.com> wrote:
>> Am 20.08.19 um 16:53 schrieb Daniel Vetter:
>>> With nouveau fixed all ttm-using drives have the correct nesting of
>>> mmap_sem vs dma_resv, and we can just lock the buffer.
>>>
>>> Assuming I didn't screw up anything with my audit of course.
>>>
>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>> Cc: Christian Koenig <christian.koenig@amd.com>
>>> Cc: Huang Rui <ray.huang@amd.com>
>>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>>> Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
>>> Cc: Thomas Hellstrom <thellstrom@vmware.com>
>> Yes, please. But one more point: you can now remove bo->wu_mutex as well!
> Ah right totally forgot about that in my enthusiasm after all the
> auditing and fixing nouveau.
>
>> Apart from that Reviewed-by: Christian König <christian.koenig@amd.com>
> Thanks, I already respun the patches, so will be in the next version.
> Can you pls also give this a spin on the amdgpu CI, just to make sure
> it's all fine? With full lockdep ofc. And then reply with a t-b.

I can ask for this on our call tomorrow, but I fear our CI 
infrastructure is not ready yet.

Christian.

>
> Thanks, Daniel
>>> ---
>>>    drivers/gpu/drm/ttm/ttm_bo.c    | 34 ---------------------------------
>>>    drivers/gpu/drm/ttm/ttm_bo_vm.c | 26 +------------------------
>>>    include/drm/ttm/ttm_bo_api.h    |  1 -
>>>    3 files changed, 1 insertion(+), 60 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index 20ff56f27aa4..a952dd624b06 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -1954,37 +1954,3 @@ void ttm_bo_swapout_all(struct ttm_bo_device *bdev)
>>>                ;
>>>    }
>>>    EXPORT_SYMBOL(ttm_bo_swapout_all);
>>> -
>>> -/**
>>> - * ttm_bo_wait_unreserved - interruptible wait for a buffer object to become
>>> - * unreserved
>>> - *
>>> - * @bo: Pointer to buffer
>>> - */
>>> -int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo)
>>> -{
>>> -     int ret;
>>> -
>>> -     /*
>>> -      * In the absense of a wait_unlocked API,
>>> -      * Use the bo::wu_mutex to avoid triggering livelocks due to
>>> -      * concurrent use of this function. Note that this use of
>>> -      * bo::wu_mutex can go away if we change locking order to
>>> -      * mmap_sem -> bo::reserve.
>>> -      */
>>> -     ret = mutex_lock_interruptible(&bo->wu_mutex);
>>> -     if (unlikely(ret != 0))
>>> -             return -ERESTARTSYS;
>>> -     if (!dma_resv_is_locked(bo->base.resv))
>>> -             goto out_unlock;
>>> -     ret = dma_resv_lock_interruptible(bo->base.resv, NULL);
>>> -     if (ret == -EINTR)
>>> -             ret = -ERESTARTSYS;
>>> -     if (unlikely(ret != 0))
>>> -             goto out_unlock;
>>> -     dma_resv_unlock(bo->base.resv);
>>> -
>>> -out_unlock:
>>> -     mutex_unlock(&bo->wu_mutex);
>>> -     return ret;
>>> -}
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> index 76eedb963693..505e1787aeea 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> @@ -125,31 +125,7 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
>>>                &bdev->man[bo->mem.mem_type];
>>>        struct vm_area_struct cvma;
>>>
>>> -     /*
>>> -      * Work around locking order reversal in fault / nopfn
>>> -      * between mmap_sem and bo_reserve: Perform a trylock operation
>>> -      * for reserve, and if it fails, retry the fault after waiting
>>> -      * for the buffer to become unreserved.
>>> -      */
>>> -     if (unlikely(!dma_resv_trylock(bo->base.resv))) {
>>> -             if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
>>> -                     if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
>>> -                             ttm_bo_get(bo);
>>> -                             up_read(&vmf->vma->vm_mm->mmap_sem);
>>> -                             (void) ttm_bo_wait_unreserved(bo);
>>> -                             ttm_bo_put(bo);
>>> -                     }
>>> -
>>> -                     return VM_FAULT_RETRY;
>>> -             }
>>> -
>>> -             /*
>>> -              * If we'd want to change locking order to
>>> -              * mmap_sem -> bo::reserve, we'd use a blocking reserve here
>>> -              * instead of retrying the fault...
>>> -              */
>>> -             return VM_FAULT_NOPAGE;
>>> -     }
>>> +     dma_resv_lock(bo->base.resv, NULL);
>>>
>>>        /*
>>>         * Refuse to fault imported pages. This should be handled
>>> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
>>> index 43c4929a2171..6b50e624e3e2 100644
>>> --- a/include/drm/ttm/ttm_bo_api.h
>>> +++ b/include/drm/ttm/ttm_bo_api.h
>>> @@ -765,7 +765,6 @@ ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
>>>    int ttm_bo_swapout(struct ttm_bo_global *glob,
>>>                        struct ttm_operation_ctx *ctx);
>>>    void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
>>> -int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo);
>>>
>>>    /**
>>>     * ttm_bo_uses_embedded_gem_object - check if the given bo uses the
>

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