[PATCH v3 21/23] drm/msm: Drop struct_mutex in madvise path

Rob Clark
2020-10-19T20:46:40Z

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@chromium.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 ebcd8e827363..4d808769e6ed 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -939,14 +939,9 @@ 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);
@@ -955,10 +950,8 @@ 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 827c7397ed12..c39ba9030001 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -673,8 +673,6 @@ 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;

@@ -691,7 +689,6 @@ 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);

@@ -771,6 +768,7 @@ 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 ffa2130ee97d..d79e7019cc88 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -190,8 +190,6 @@ 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