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

[Daniel Vetter]

On Tue, Aug 20, 2019 at 5:16 PM Koenig, Christian
<Christian.Koenig at 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 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>
>
> 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 at 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.

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
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch