Re: [PATCH v1] drm/gem-vram: Fix deadlock in drm_gem_vram_vmap()

[Christian König]

Am 14.11.22 um 00:38 schrieb Dmitry Osipenko:

Recently DRM framebuffer core and all drivers were moved to unlocked
vmapping functions that take the reservation lock. The drm_gem_vram_vmap()
was missed out by accident and now deadlocks drivers that use drm_gem_vram
helpers when framebuffer is updated, like Bochs driver. Remove the locking
from drm_gem_vram_v[un]map() functions to fix the deadlock.

Reported-by: Dmitry Vyukov <dvyu...@google.com>
Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap 
operations")
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>

Reviewed-by: Christian König <christian.koe...@amd.com

---
  drivers/gpu/drm/drm_gem_vram_helper.c | 18 +++---------------
  1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c 
b/drivers/gpu/drm/drm_gem_vram_helper.c
index 125160b534be..b6c7e3803bb3 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -433,25 +433,19 @@ int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, 
struct iosys_map *map)
  {
        int ret;

- ret = ttm_bo_reserve(&gbo->bo, true, false, NULL);

-       if (ret)
-               return ret;
+       dma_resv_assert_held(gbo->bo.base.resv);

ret = drm_gem_vram_pin_locked(gbo, 0);

        if (ret)
-               goto err_ttm_bo_unreserve;
+               return ret;
        ret = drm_gem_vram_kmap_locked(gbo, map);
        if (ret)
                goto err_drm_gem_vram_unpin_locked;

- ttm_bo_unreserve(&gbo->bo);

-
        return 0;

err_drm_gem_vram_unpin_locked:

        drm_gem_vram_unpin_locked(gbo);
-err_ttm_bo_unreserve:
-       ttm_bo_unreserve(&gbo->bo);
        return ret;
  }
  EXPORT_SYMBOL(drm_gem_vram_vmap);
@@ -467,16 +461,10 @@ EXPORT_SYMBOL(drm_gem_vram_vmap);
  void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo,
                         struct iosys_map *map)
  {
-       int ret;
-
-       ret = ttm_bo_reserve(&gbo->bo, false, false, NULL);
-       if (WARN_ONCE(ret, "ttm_bo_reserve_failed(): ret=%d\n", ret))
-               return;
+       dma_resv_assert_held(gbo->bo.base.resv);

drm_gem_vram_kunmap_locked(gbo, map);

        drm_gem_vram_unpin_locked(gbo);
-
-       ttm_bo_unreserve(&gbo->bo);
  }
  EXPORT_SYMBOL(drm_gem_vram_vunmap);