From: Rob Clark <robdclark@gmail.com> To: dri-devel@lists.freedesktop.org Cc: Rob Clark <robdclark@chromium.org>, David Airlie <airlied@linux.ie>, linux-arm-msm@vger.kernel.org, Abhinav Kumar <quic_abhinavk@quicinc.com>, open list <linux-kernel@vger.kernel.org>, Sean Paul <sean@poorly.run>, Dmitry Baryshkov <dmitry.baryshkov@linaro.org>, freedreno@lists.freedesktop.org Subject: [PATCH] drm/msm/gem: Drop obj lock in msm_gem_free_object() Date: Mon, 13 Jun 2022 13:50:32 -0700 [thread overview] Message-ID: <20220613205032.2652374-1-robdclark@gmail.com> (raw) From: Rob Clark <robdclark@chromium.org> The only reason we grabbed the lock was to satisfy a bunch of places that WARN_ON() if called without the lock held. But this angers lockdep which doesn't realize no one else can be holding the lock by the time we end up destroying the object (and sees what would otherwise be a locking inversion between reservation_ww_class_mutex and fs_reclaim). Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/14 Signed-off-by: Rob Clark <robdclark@chromium.org> --- drivers/gpu/drm/msm/msm_gem.c | 8 -------- drivers/gpu/drm/msm/msm_gem.h | 14 +++++++++++++- 2 files changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index 3ef7ada59392..ccc7e6d8cc30 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -1020,8 +1020,6 @@ static void msm_gem_free_object(struct drm_gem_object *obj) list_del(&msm_obj->mm_list); mutex_unlock(&priv->mm_lock); - msm_gem_lock(obj); - /* object should not be on active list: */ GEM_WARN_ON(is_active(msm_obj)); @@ -1037,17 +1035,11 @@ static void msm_gem_free_object(struct drm_gem_object *obj) put_iova_vmas(obj); - /* dma_buf_detach() grabs resv lock, so we need to unlock - * prior to drm_prime_gem_destroy - */ - msm_gem_unlock(obj); - drm_prime_gem_destroy(obj, msm_obj->sgt); } else { msm_gem_vunmap(obj); put_pages(obj); put_iova_vmas(obj); - msm_gem_unlock(obj); } drm_gem_object_release(obj); diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h index d608339c1643..432032ad4aed 100644 --- a/drivers/gpu/drm/msm/msm_gem.h +++ b/drivers/gpu/drm/msm/msm_gem.h @@ -229,7 +229,19 @@ msm_gem_unlock(struct drm_gem_object *obj) static inline bool msm_gem_is_locked(struct drm_gem_object *obj) { - return dma_resv_is_locked(obj->resv); + /* + * Destroying the object is a special case.. msm_gem_free_object() + * calls many things that WARN_ON if the obj lock is not held. But + * acquiring the obj lock in msm_gem_free_object() can cause a + * locking order inversion between reservation_ww_class_mutex and + * fs_reclaim. + * + * This deadlock is not actually possible, because no one should + * be already holding the lock when msm_gem_free_object() is called. + * Unfortunately lockdep is not aware of this detail. So when the + * refcount drops to zero, we pretend it is already locked. + */ + return dma_resv_is_locked(obj->resv) || (kref_read(&obj->refcount) == 0); } static inline bool is_active(struct msm_gem_object *msm_obj) -- 2.36.1
WARNING: multiple messages have this Message-ID (diff)
From: Rob Clark <robdclark@gmail.com> To: dri-devel@lists.freedesktop.org Cc: freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, Rob Clark <robdclark@chromium.org>, Rob Clark <robdclark@gmail.com>, Abhinav Kumar <quic_abhinavk@quicinc.com>, Dmitry Baryshkov <dmitry.baryshkov@linaro.org>, Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org (open list) Subject: [PATCH] drm/msm/gem: Drop obj lock in msm_gem_free_object() Date: Mon, 13 Jun 2022 13:50:32 -0700 [thread overview] Message-ID: <20220613205032.2652374-1-robdclark@gmail.com> (raw) From: Rob Clark <robdclark@chromium.org> The only reason we grabbed the lock was to satisfy a bunch of places that WARN_ON() if called without the lock held. But this angers lockdep which doesn't realize no one else can be holding the lock by the time we end up destroying the object (and sees what would otherwise be a locking inversion between reservation_ww_class_mutex and fs_reclaim). Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/14 Signed-off-by: Rob Clark <robdclark@chromium.org> --- drivers/gpu/drm/msm/msm_gem.c | 8 -------- drivers/gpu/drm/msm/msm_gem.h | 14 +++++++++++++- 2 files changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index 3ef7ada59392..ccc7e6d8cc30 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -1020,8 +1020,6 @@ static void msm_gem_free_object(struct drm_gem_object *obj) list_del(&msm_obj->mm_list); mutex_unlock(&priv->mm_lock); - msm_gem_lock(obj); - /* object should not be on active list: */ GEM_WARN_ON(is_active(msm_obj)); @@ -1037,17 +1035,11 @@ static void msm_gem_free_object(struct drm_gem_object *obj) put_iova_vmas(obj); - /* dma_buf_detach() grabs resv lock, so we need to unlock - * prior to drm_prime_gem_destroy - */ - msm_gem_unlock(obj); - drm_prime_gem_destroy(obj, msm_obj->sgt); } else { msm_gem_vunmap(obj); put_pages(obj); put_iova_vmas(obj); - msm_gem_unlock(obj); } drm_gem_object_release(obj); diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h index d608339c1643..432032ad4aed 100644 --- a/drivers/gpu/drm/msm/msm_gem.h +++ b/drivers/gpu/drm/msm/msm_gem.h @@ -229,7 +229,19 @@ msm_gem_unlock(struct drm_gem_object *obj) static inline bool msm_gem_is_locked(struct drm_gem_object *obj) { - return dma_resv_is_locked(obj->resv); + /* + * Destroying the object is a special case.. msm_gem_free_object() + * calls many things that WARN_ON if the obj lock is not held. But + * acquiring the obj lock in msm_gem_free_object() can cause a + * locking order inversion between reservation_ww_class_mutex and + * fs_reclaim. + * + * This deadlock is not actually possible, because no one should + * be already holding the lock when msm_gem_free_object() is called. + * Unfortunately lockdep is not aware of this detail. So when the + * refcount drops to zero, we pretend it is already locked. + */ + return dma_resv_is_locked(obj->resv) || (kref_read(&obj->refcount) == 0); } static inline bool is_active(struct msm_gem_object *msm_obj) -- 2.36.1
next reply other threads:[~2022-06-13 20:50 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-13 20:50 Rob Clark [this message] 2022-06-13 20:50 ` [PATCH] drm/msm/gem: Drop obj lock in msm_gem_free_object() Rob Clark 2022-06-16 8:28 ` Stephen Boyd 2022-06-16 8:28 ` Stephen Boyd 2022-06-16 13:59 ` Rob Clark 2022-06-16 13:59 ` Rob Clark 2022-06-24 20:58 ` Daniel Vetter 2022-06-24 20:58 ` Daniel Vetter 2022-06-24 21:28 ` Rob Clark 2022-06-24 21:28 ` Rob Clark 2022-06-24 21:36 ` Daniel Vetter 2022-06-24 21:36 ` Daniel Vetter 2022-06-24 21:49 ` Rob Clark 2022-06-24 21:49 ` Rob Clark
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