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    Subject[PATCH 5.11 073/120] drm/ttm: Warn on pinning without holding a reference
    Date
    From: Daniel Vetter <daniel.vetter@ffwll.ch>

    [ Upstream commit 57fcd550eb15bce14a7154736379dfd4ed60ae81 ]

    Not technically a problem for ttm, but very likely a driver bug and
    pretty big time confusing for reviewing code.

    So warn about it, both at cleanup time (so we catch these for sure)
    and at pin/unpin time (so we know who's the culprit).

    Reviewed-by: Huang Rui <ray.huang@amd.com>
    Reviewed-by: Christian König <christian.koenig@amd.com>
    Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
    Cc: Christian Koenig <christian.koenig@amd.com>
    Cc: Huang Rui <ray.huang@amd.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20201028113120.3641237-1-daniel.vetter@ffwll.ch
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/ttm/ttm_bo.c | 2 +-
    include/drm/ttm/ttm_bo_api.h | 2 ++
    2 files changed, 3 insertions(+), 1 deletion(-)

    diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
    index 22073e77fdf9..a76eb2c14e8c 100644
    --- a/drivers/gpu/drm/ttm/ttm_bo.c
    +++ b/drivers/gpu/drm/ttm/ttm_bo.c
    @@ -514,7 +514,7 @@ static void ttm_bo_release(struct kref *kref)
    * shrinkers, now that they are queued for
    * destruction.
    */
    - if (bo->pin_count) {
    + if (WARN_ON(bo->pin_count)) {
    bo->pin_count = 0;
    ttm_bo_del_from_lru(bo);
    ttm_bo_add_mem_to_lru(bo, &bo->mem);
    diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
    index 2564e66e67d7..79b9367e0ffd 100644
    --- a/include/drm/ttm/ttm_bo_api.h
    +++ b/include/drm/ttm/ttm_bo_api.h
    @@ -600,6 +600,7 @@ static inline bool ttm_bo_uses_embedded_gem_object(struct ttm_buffer_object *bo)
    static inline void ttm_bo_pin(struct ttm_buffer_object *bo)
    {
    dma_resv_assert_held(bo->base.resv);
    + WARN_ON_ONCE(!kref_read(&bo->kref));
    ++bo->pin_count;
    }

    @@ -613,6 +614,7 @@ static inline void ttm_bo_unpin(struct ttm_buffer_object *bo)
    {
    dma_resv_assert_held(bo->base.resv);
    WARN_ON_ONCE(!bo->pin_count);
    + WARN_ON_ONCE(!kref_read(&bo->kref));
    --bo->pin_count;
    }

    --
    2.30.1


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