[Intel-gfx] [PATCH] drm/ttm: remove ttm_bo_wait_unreserved
Thomas Hellström (VMware)
thomas_os at shipmail.org
Thu Aug 22 14:24:49 UTC 2019
On 8/22/19 4:02 PM, Koenig, Christian wrote:
> Am 22.08.19 um 15:06 schrieb Daniel Vetter:
>> On Thu, Aug 22, 2019 at 07:56:56AM +0000, Koenig, Christian wrote:
>>> Am 22.08.19 um 08:49 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.
>>>>
>>>> v2:
>>>> - Dont forget wu_mutex (Christian König)
>>>> - Keep the mmap_sem-less wait optimization (Thomas)
>>>> - Use _lock_interruptible to be good citizens (Thomas)
>>>>
>>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>> btw I realized I didn't remove your r-b, since v1 was broken.
>>
>> For formality, can you pls reaffirm, or still something broken?
> My r-b is still valid.
>
> Only problem I see is that neither of us seems to have a good idea about
> the different VM_FAULT_* replies.
I took a look in mm/gup.c. It seems like when using get_user_pages,
VM_FAULT_RETRY will retry to a requesting caller telling it that a long
wait was expected and not performed, whereas VM_FAULT_NOPAGE will just
keep get_user_pages to spin. So the proposed patch should be correct
from my understanding.
If the fault originates from user-space, I guess either is fine.
/Thomas
>
> But that worked before so it should still work now,
> Christian.
>
>> Also from the other thread: Reviewed-by: Thomas Hellström <thellstrom at vmware.com>
>>
>> Thanks, Daniel
>>
>>>> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
>>>> Cc: Christian Koenig <christian.koenig at amd.com>
>>>> Cc: Huang Rui <ray.huang at amd.com>
>>>> Cc: Gerd Hoffmann <kraxel at redhat.com>
>>>> Cc: "VMware Graphics" <linux-graphics-maintainer at vmware.com>
>>>> Cc: Thomas Hellstrom <thellstrom at vmware.com>
>>>> ---
>>>> drivers/gpu/drm/ttm/ttm_bo.c | 36 -------------------------------
>>>> drivers/gpu/drm/ttm/ttm_bo_util.c | 1 -
>>>> drivers/gpu/drm/ttm/ttm_bo_vm.c | 18 +++++-----------
>>>> include/drm/ttm/ttm_bo_api.h | 4 ----
>>>> 4 files changed, 5 insertions(+), 54 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>>> index 20ff56f27aa4..d1ce5d315d5b 100644
>>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>>> @@ -162,7 +162,6 @@ static void ttm_bo_release_list(struct kref *list_kref)
>>>> dma_fence_put(bo->moving);
>>>> if (!ttm_bo_uses_embedded_gem_object(bo))
>>>> dma_resv_fini(&bo->base._resv);
>>>> - mutex_destroy(&bo->wu_mutex);
>>>> bo->destroy(bo);
>>>> ttm_mem_global_free(bdev->glob->mem_glob, acc_size);
>>>> }
>>>> @@ -1319,7 +1318,6 @@ int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
>>>> INIT_LIST_HEAD(&bo->ddestroy);
>>>> INIT_LIST_HEAD(&bo->swap);
>>>> INIT_LIST_HEAD(&bo->io_reserve_lru);
>>>> - mutex_init(&bo->wu_mutex);
>>>> bo->bdev = bdev;
>>>> bo->type = type;
>>>> bo->num_pages = num_pages;
>>>> @@ -1954,37 +1952,3 @@ 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_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
>>>> index fe81c565e7ef..82ea26a49959 100644
>>>> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
>>>> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
>>>> @@ -508,7 +508,6 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>>>> INIT_LIST_HEAD(&fbo->base.lru);
>>>> INIT_LIST_HEAD(&fbo->base.swap);
>>>> INIT_LIST_HEAD(&fbo->base.io_reserve_lru);
>>>> - mutex_init(&fbo->base.wu_mutex);
>>>> fbo->base.moving = NULL;
>>>> drm_vma_node_reset(&fbo->base.base.vma_node);
>>>> atomic_set(&fbo->base.cpu_writers, 0);
>>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>>> index 76eedb963693..a61a35e57d1c 100644
>>>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>>> @@ -125,30 +125,22 @@ 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)) {
>>> Not an expert on fault handling, but shouldn't this now be one if?
>>>
>>> E.g. if FAULT_FLAG_RETRY_NOWAIT is set we should return VM_FAULT_NOPAGE
>>> instead of VM_FAULT_RETRY.
>>>
>>> But really take that with a grain of salt,
>>> Christian.
>>>
>>>> ttm_bo_get(bo);
>>>> up_read(&vmf->vma->vm_mm->mmap_sem);
>>>> - (void) ttm_bo_wait_unreserved(bo);
>>>> + if (!dma_resv_lock_interruptible(bo->base.resv,
>>>> + NULL))
>>>> + dma_resv_unlock(bo->base.resv);
>>>> 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;
>>>> + if (dma_resv_lock_interruptible(bo->base.resv, NULL))
>>>> + return VM_FAULT_NOPAGE;
>>>> }
>>>>
>>>> /*
>>>> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
>>>> index 43c4929a2171..21c7d0d28757 100644
>>>> --- a/include/drm/ttm/ttm_bo_api.h
>>>> +++ b/include/drm/ttm/ttm_bo_api.h
>>>> @@ -155,7 +155,6 @@ struct ttm_tt;
>>>> * @offset: The current GPU offset, which can have different meanings
>>>> * depending on the memory type. For SYSTEM type memory, it should be 0.
>>>> * @cur_placement: Hint of current placement.
>>>> - * @wu_mutex: Wait unreserved mutex.
>>>> *
>>>> * Base class for TTM buffer object, that deals with data placement and CPU
>>>> * mappings. GPU mappings are really up to the driver, but for simpler GPUs
>>>> @@ -229,8 +228,6 @@ struct ttm_buffer_object {
>>>> uint64_t offset; /* GPU address space is independent of CPU word size */
>>>>
>>>> struct sg_table *sg;
>>>> -
>>>> - struct mutex wu_mutex;
>>>> };
>>>>
>>>> /**
>>>> @@ -765,7 +762,6 @@ 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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