linux-kernel - [PATCH v2 20/22] drm/msm: drop struct

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Date:   Sun, 11 Oct 2020 19:09:47 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm@...r.kernel.org (open list:DRM DRIVER FOR MSM ADRENO GPU),
        freedreno@...ts.freedesktop.org (open list:DRM DRIVER FOR MSM ADRENO
        GPU), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 20/22] drm/msm: drop struct_mutex in madvise path

From: Rob Clark <robdclark@...omium.org>

The obj->lock is sufficient for what we need.

This *does* have the implication that userspace can try to shoot
themselves in the foot by racing madvise(DONTNEED) with submit.  But
the result will be about the same if they did madvise(DONTNEED) before
the submit ioctl, ie. they might not get want they want if they race
with shrinker.  But iova fault handling is robust enough, and userspace
is only shooting it's own foot.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/msm_drv.c | 11 ++---------
 drivers/gpu/drm/msm/msm_gem.c |  4 +---
 drivers/gpu/drm/msm/msm_gem.h |  2 --
 3 files changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 49e6daf30b42..f2d58fe25497 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -912,14 +912,9 @@ static int msm_ioctl_gem_madvise(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
-	if (ret)
-		return ret;
-
 	obj = drm_gem_object_lookup(file, args->handle);
 	if (!obj) {
-		ret = -ENOENT;
-		goto unlock;
+		return -ENOENT;
 	}
 
 	ret = msm_gem_madvise(obj, args->madv);
@@ -928,10 +923,8 @@ static int msm_ioctl_gem_madvise(struct drm_device *dev, void *data,
 		ret = 0;
 	}
 
-	drm_gem_object_put_locked(obj);
+	drm_gem_object_put(obj);
 
-unlock:
-	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index b60eaf6266e2..8852c05775dc 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -658,8 +658,6 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)
 
 	msm_gem_lock(obj);
 
-	WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
-
 	if (msm_obj->madv != __MSM_MADV_PURGED)
 		msm_obj->madv = madv;
 
@@ -676,7 +674,6 @@ void msm_gem_purge(struct drm_gem_object *obj)
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
 	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-	WARN_ON(!msm_gem_is_locked(obj));
 	WARN_ON(!is_purgeable(msm_obj));
 	WARN_ON(obj->import_attach);
 
@@ -756,6 +753,7 @@ void msm_gem_active_get(struct drm_gem_object *obj, struct msm_gpu *gpu)
 	struct msm_drm_private *priv = obj->dev->dev_private;
 
 	might_sleep();
+	WARN_ON(!msm_gem_is_locked(obj));
 	WARN_ON(msm_obj->madv != MSM_MADV_WILLNEED);
 
 	if (!atomic_fetch_inc(&msm_obj->active_count)) {
diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index c12fedf88e85..1f8f5f3d08c0 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -188,8 +188,6 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
 
 static inline bool is_purgeable(struct msm_gem_object *msm_obj)
 {
-	WARN_ON(!msm_gem_is_locked(&msm_obj->base));
-	WARN_ON(!mutex_is_locked(&msm_obj->base.dev->struct_mutex));
 	return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
 			!msm_obj->base.dma_buf && !msm_obj->base.import_attach;
 }
-- 
2.26.2