On Thu, Jan 7, 2021 at 11:28 AM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
>
> Hi Daniel
>
> Am 11.12.20 um 10:50 schrieb Daniel Vetter:
> [...]
> >> +/**
> >> + * drm_gem_shmem_vmap_local - Create a virtual mapping for a shmem GEM object
> >> + * @shmem: shmem GEM object
> >> + * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
> >> + * store.
> >> + *
> >> + * This function makes sure that a contiguous kernel virtual address mapping
> >> + * exists for the buffer backing the shmem GEM object.
> >> + *
> >> + * The function is called with the BO's reservation object locked. Callers must
> >> + * hold the lock until after unmapping the buffer.
> >> + *
> >> + * This function can be used to implement &drm_gem_object_funcs.vmap_local. But
> >> + * it can also be called by drivers directly, in which case it will hide the
> >> + * differences between dma-buf imported and natively allocated objects.
> >> + *
> >> + * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap_local().
> >> + *
> >> + * Returns:
> >> + * 0 on success or a negative error code on failure.
> >> + */
> >> +int drm_gem_shmem_vmap_local(struct drm_gem_object *obj, struct dma_buf_map *map)
> >> +{
> >> + struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >> + int ret;
> >> +
> >> + dma_resv_assert_held(obj->resv);
> >> +
> >> + ret = mutex_lock_interruptible(&shmem->vmap_lock);
> >
> > This bites. You need to check for shmem->import_attach and call
> > dma_buf_vmap_local directly here before you take any shmem helper locks.
> > Real fix would be to replace both vmap_lock and pages_lock with dma_resv
> > lock, but that's more work. Same for vunmap_local
>
> This comment confuses me. AFAICT vmap_lock protects vmap_use_count. Why
> does this exact code work in drm_gem_shmem_vmap() but not in _local() ?
You'd hold the dma_resv lock both inside and outside of the
->vmap_lock mutex. Which deadlocks. For the _vmap version we more or
less mandate that the caller doens't hold the dma_resv lock already,
hence why we can get away with that.
-Daniel
> Best regards
> Thomas
>
> >
> > With that fixed on the helper part of this patch:
> >
> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> >
> >
> >> + if (ret)
> >> + return ret;
> >> + ret = drm_gem_shmem_vmap_locked(shmem, map);
> >> + mutex_unlock(&shmem->vmap_lock);
> >> +
> >> + return ret;
> >> +}
> >> +EXPORT_SYMBOL(drm_gem_shmem_vmap_local);
> >> +
> >> static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
> >> struct dma_buf_map *map)
> >> {
> >> @@ -366,7 +406,7 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
> >> drm_gem_shmem_put_pages(shmem);
> >> }
> >>
> >> -/*
> >> +/**
> >> * drm_gem_shmem_vunmap - Unmap a virtual mapping fo a shmem GEM object
> >> * @shmem: shmem GEM object
> >> * @map: Kernel virtual address where the SHMEM GEM object was mapped
> >> @@ -389,6 +429,33 @@ void drm_gem_shmem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
> >> }
> >> EXPORT_SYMBOL(drm_gem_shmem_vunmap);
> >>
> >> +/**
> >> + * drm_gem_shmem_vunmap_local - Unmap a virtual mapping fo a shmem GEM object
> >> + * @shmem: shmem GEM object
> >> + * @map: Kernel virtual address where the SHMEM GEM object was mapped
> >> + *
> >> + * This function cleans up a kernel virtual address mapping acquired by
> >> + * drm_gem_shmem_vmap_local(). The mapping is only removed when the use count
> >> + * drops to zero.
> >> + *
> >> + * The function is called with the BO's reservation object locked.
> >> + *
> >> + * This function can be used to implement &drm_gem_object_funcs.vmap_local.
> >> + * But it can also be called by drivers directly, in which case it will hide
> >> + * the differences between dma-buf imported and natively allocated objects.
> >> + */
> >> +void drm_gem_shmem_vunmap_local(struct drm_gem_object *obj, struct dma_buf_map *map)
> >> +{
> >> + struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >> +
> >> + dma_resv_assert_held(obj->resv);
> >> +
> >> + mutex_lock(&shmem->vmap_lock);
> >> + drm_gem_shmem_vunmap_locked(shmem, map);
> >> + mutex_unlock(&shmem->vmap_lock);
> >> +}
> >> +EXPORT_SYMBOL(drm_gem_shmem_vunmap_local);
> >> +
> >> struct drm_gem_shmem_object *
> >> drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
> >> struct drm_device *dev, size_t size,
> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> index 1dfc42170059..a33e28d4c5e9 100644
> >> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> @@ -1552,22 +1552,32 @@ mgag200_handle_damage(struct mga_device *mdev, struct drm_framebuffer *fb,
> >> struct drm_rect *clip)
> >> {
> >> struct drm_device *dev = &mdev->base;
> >> + struct drm_gem_object *obj = fb->obj[0];
> >> struct dma_buf_map map;
> >> void *vmap;
> >> int ret;
> >>
> >> - ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> >> + ret = dma_resv_lock(obj->resv, NULL);
> >> if (drm_WARN_ON(dev, ret))
> >> - return; /* BUG: SHMEM BO should always be vmapped */
> >> + return;
> >> + ret = drm_gem_shmem_vmap_local(obj, &map);
> >> + if (drm_WARN_ON(dev, ret))
> >> + goto err_dma_resv_unlock; /* BUG: SHMEM BO should always be vmapped */
> >> vmap = map.vaddr; /* TODO: Use mapping abstraction properly */
> >>
> >> drm_fb_memcpy_dstclip(mdev->vram, vmap, fb, clip);
> >>
> >> - drm_gem_shmem_vunmap(fb->obj[0], &map);
> >> + drm_gem_shmem_vunmap_local(obj, &map);
> >> + dma_resv_unlock(obj->resv);
> >>
> >> /* Always scanout image at VRAM offset 0 */
> >> mgag200_set_startadd(mdev, (u32)0);
> >> mgag200_set_offset(mdev, fb);
> >> +
> >> + return;
> >> +
> >> +err_dma_resv_unlock:
> >> + dma_resv_unlock(obj->resv);
> >> }
> >>
> >> static void
> >> diff --git a/drivers/gpu/drm/tiny/cirrus.c b/drivers/gpu/drm/tiny/cirrus.c
> >> index 561c49d8657a..58c694964148 100644
> >> --- a/drivers/gpu/drm/tiny/cirrus.c
> >> +++ b/drivers/gpu/drm/tiny/cirrus.c
> >> @@ -315,6 +315,7 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >> struct drm_rect *rect)
> >> {
> >> struct cirrus_device *cirrus = to_cirrus(fb->dev);
> >> + struct drm_gem_object *obj = fb->obj[0];
> >> struct dma_buf_map map;
> >> void *vmap;
> >> int idx, ret;
> >> @@ -323,9 +324,12 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >> if (!drm_dev_enter(&cirrus->dev, &idx))
> >> goto out;
> >>
> >> - ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> >> + ret = dma_resv_lock(obj->resv, NULL);
> >> if (ret)
> >> goto out_dev_exit;
> >> + ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> >> + if (ret)
> >> + goto out_dma_resv_unlock;
> >> vmap = map.vaddr; /* TODO: Use mapping abstraction properly */
> >>
> >> if (cirrus->cpp == fb->format->cpp[0])
> >> @@ -345,9 +349,11 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >> else
> >> WARN_ON_ONCE("cpp mismatch");
> >>
> >> - drm_gem_shmem_vunmap(fb->obj[0], &map);
> >> ret = 0;
> >>
> >> + drm_gem_shmem_vunmap_local(obj, &map);
> >> +out_dma_resv_unlock:
> >> + dma_resv_unlock(obj->resv);
> >> out_dev_exit:
> >> drm_dev_exit(idx);
> >> out:
> >> diff --git a/drivers/gpu/drm/tiny/gm12u320.c b/drivers/gpu/drm/tiny/gm12u320.c
> >> index 33f65f4626e5..b0c6e350f2b3 100644
> >> --- a/drivers/gpu/drm/tiny/gm12u320.c
> >> +++ b/drivers/gpu/drm/tiny/gm12u320.c
> >> @@ -265,11 +265,16 @@ static void gm12u320_copy_fb_to_blocks(struct gm12u320_device *gm12u320)
> >> y1 = gm12u320->fb_update.rect.y1;
> >> y2 = gm12u320->fb_update.rect.y2;
> >>
> >> - ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> >> + ret = dma_resv_lock(fb->obj[0]->resv, NULL);
> >> if (ret) {
> >> - GM12U320_ERR("failed to vmap fb: %d\n", ret);
> >> + GM12U320_ERR("failed to reserve fb: %d\n", ret);
> >> goto put_fb;
> >> }
> >> + ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> >> + if (ret) {
> >> + GM12U320_ERR("failed to vmap fb: %d\n", ret);
> >> + goto unlock_resv;
> >> + }
> >> vaddr = map.vaddr; /* TODO: Use mapping abstraction properly */
> >>
> >> if (fb->obj[0]->import_attach) {
> >> @@ -321,8 +326,11 @@ static void gm12u320_copy_fb_to_blocks(struct gm12u320_device *gm12u320)
> >> if (ret)
> >> GM12U320_ERR("dma_buf_end_cpu_access err: %d\n", ret);
> >> }
> >> +
> >> +unlock_resv:
> >> + dma_resv_unlock(fb->obj[0]->resv);
> >> vunmap:
> >> - drm_gem_shmem_vunmap(fb->obj[0], &map);
> >> + drm_gem_shmem_vunmap_local(fb->obj[0], &map);
> >> put_fb:
> >> drm_framebuffer_put(fb);
> >> gm12u320->fb_update.fb = NULL;
> >> diff --git a/drivers/gpu/drm/udl/udl_modeset.c b/drivers/gpu/drm/udl/udl_modeset.c
> >> index 9d34ec9d03f6..46b55b4d03c2 100644
> >> --- a/drivers/gpu/drm/udl/udl_modeset.c
> >> +++ b/drivers/gpu/drm/udl/udl_modeset.c
> >> @@ -290,14 +290,18 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >> else if ((clip.x2 > fb->width) || (clip.y2 > fb->height))
> >> return -EINVAL;
> >>
> >> + ret = dma_resv_lock(fb->obj[0]->resv, NULL);
> >> + if (ret)
> >> + return ret;
> >> +
> >> if (import_attach) {
> >> ret = dma_buf_begin_cpu_access(import_attach->dmabuf,
> >> DMA_FROM_DEVICE);
> >> if (ret)
> >> - return ret;
> >> + goto out_dma_resv_unlock;
> >> }
> >>
> >> - ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> >> + ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> >> if (ret) {
> >> DRM_ERROR("failed to vmap fb\n");
> >> goto out_dma_buf_end_cpu_access;
> >> @@ -307,7 +311,7 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >> urb = udl_get_urb(dev);
> >> if (!urb) {
> >> ret = -ENOMEM;
> >> - goto out_drm_gem_shmem_vunmap;
> >> + goto out_drm_gem_shmem_vunmap_local;
> >> }
> >> cmd = urb->transfer_buffer;
> >>
> >> @@ -320,7 +324,7 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >> &cmd, byte_offset, dev_byte_offset,
> >> byte_width);
> >> if (ret)
> >> - goto out_drm_gem_shmem_vunmap;
> >> + goto out_drm_gem_shmem_vunmap_local;
> >> }
> >>
> >> if (cmd > (char *)urb->transfer_buffer) {
> >> @@ -336,8 +340,8 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >>
> >> ret = 0;
> >>
> >> -out_drm_gem_shmem_vunmap:
> >> - drm_gem_shmem_vunmap(fb->obj[0], &map);
> >> +out_drm_gem_shmem_vunmap_local:
> >> + drm_gem_shmem_vunmap_local(fb->obj[0], &map);
> >> out_dma_buf_end_cpu_access:
> >> if (import_attach) {
> >> tmp_ret = dma_buf_end_cpu_access(import_attach->dmabuf,
> >> @@ -345,6 +349,8 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >> if (tmp_ret && !ret)
> >> ret = tmp_ret; /* only update ret if not set yet */
> >> }
> >> +out_dma_resv_unlock:
> >> + dma_resv_unlock(fb->obj[0]->resv);
> >>
> >> return ret;
> >> }
> >> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> >> index 434328d8a0d9..3f59bdf749aa 100644
> >> --- a/include/drm/drm_gem_shmem_helper.h
> >> +++ b/include/drm/drm_gem_shmem_helper.h
> >> @@ -114,7 +114,9 @@ void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem);
> >> int drm_gem_shmem_pin(struct drm_gem_object *obj);
> >> void drm_gem_shmem_unpin(struct drm_gem_object *obj);
> >> int drm_gem_shmem_vmap(struct drm_gem_object *obj, struct dma_buf_map *map);
> >> +int drm_gem_shmem_vmap_local(struct drm_gem_object *obj, struct dma_buf_map *map);
> >> void drm_gem_shmem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map);
> >> +void drm_gem_shmem_vunmap_local(struct drm_gem_object *obj, struct dma_buf_map *map);
> >>
> >> int drm_gem_shmem_madvise(struct drm_gem_object *obj, int madv);
> >>
> >> --
> >> 2.29.2
> >>
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
