[PATCH v2 3/4] drm/msm: Fix debugfs deadlock

Rob Clark
2021-04-01T01:24:36Z

From: Rob Clark <robdclark@chromium.org>

In normal cases the gem obj lock is acquired first before mm_lock. The
exception is iterating the various object lists. In the shrinker path,
deadlock is avoided by using msm_gem_trylock() and skipping over objects
that cannot be locked. But for debugfs the straightforward thing is to
split things out into a separate list of all objects protected by it's
own lock.

Fixes: d984457b31c4 ("drm/msm: Add priv->mm_lock to protect active/inactive lists")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
---
drivers/gpu/drm/msm/msm_debugfs.c | 14 +++-----------
drivers/gpu/drm/msm/msm_drv.c | 3 +++
drivers/gpu/drm/msm/msm_drv.h | 9 ++++++++-
drivers/gpu/drm/msm/msm_gem.c | 14 +++++++++++++-
drivers/gpu/drm/msm/msm_gem.h | 10 ++++++++--
5 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_debugfs.c b/drivers/gpu/drm/msm/msm_debugfs.c
index 85ad0babc326..d611cc8e54a4 100644
--- a/drivers/gpu/drm/msm/msm_debugfs.c
+++ b/drivers/gpu/drm/msm/msm_debugfs.c
@@ -111,23 +111,15 @@ static const struct file_operations msm_gpu_fops = {
static int msm_gem_show(struct drm_device *dev, struct seq_file *m)
{
struct msm_drm_private *priv = dev->dev_private;
- struct msm_gpu *gpu = priv->gpu;
int ret;

- ret = mutex_lock_interruptible(&priv->mm_lock);
+ ret = mutex_lock_interruptible(&priv->obj_lock);
if (ret)
return ret;

- if (gpu) {
- seq_printf(m, "Active Objects (%s):\n", gpu->name);
- msm_gem_describe_objects(&gpu->active_list, m);
- }
-
- seq_printf(m, "Inactive Objects:\n");
- msm_gem_describe_objects(&priv->inactive_dontneed, m);
- msm_gem_describe_objects(&priv->inactive_willneed, m);
+ msm_gem_describe_objects(&priv->objects, m);

- mutex_unlock(&priv->mm_lock);
+ mutex_unlock(&priv->obj_lock);

return 0;
}
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 3462b0ea14c6..1ef1cd0cc714 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -474,6 +474,9 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)

priv->wq = alloc_ordered_workqueue("msm", 0);

+ INIT_LIST_HEAD(&priv->objects);
+ mutex_init(&priv->obj_lock);
+
INIT_LIST_HEAD(&priv->inactive_willneed);
INIT_LIST_HEAD(&priv->inactive_dontneed);
INIT_LIST_HEAD(&priv->inactive_purged);
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index 503168817e24..c84e6f84cb6d 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -174,7 +174,14 @@ struct msm_drm_private {
struct msm_rd_state *hangrd; /* debugfs to dump hanging submits */
struct msm_perf_state *perf;

- /*
+ /**
+ * List of all GEM objects (mainly for debugfs, protected by obj_lock
+ * (acquire before per GEM object lock)
+ */
+ struct list_head objects;
+ struct mutex obj_lock;
+
+ /**
* Lists of inactive GEM objects. Every bo is either in one of the
* inactive lists (depending on whether or not it is shrinkable) or
* gpu->active_list (for the gpu it is active on[1])
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index bec01bb48fce..7ca30e362222 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -961,7 +961,7 @@ void msm_gem_describe_objects(struct list_head *list, struct seq_file *m)
size_t size = 0;

seq_puts(m, " flags id ref offset kaddr size madv name\n");
- list_for_each_entry(msm_obj, list, mm_list) {
+ list_for_each_entry(msm_obj, list, node) {
struct drm_gem_object *obj = &msm_obj->base;
seq_puts(m, " ");
msm_gem_describe(obj, m);
@@ -980,6 +980,10 @@ void msm_gem_free_object(struct drm_gem_object *obj)
struct drm_device *dev = obj->dev;
struct msm_drm_private *priv = dev->dev_private;

+ mutex_lock(&priv->obj_lock);
+ list_del(&msm_obj->node);
+ mutex_unlock(&priv->obj_lock);
+
mutex_lock(&priv->mm_lock);
if (msm_obj->dontneed)
mark_unpurgable(msm_obj);
@@ -1170,6 +1174,10 @@ static struct drm_gem_object *_msm_gem_new(struct drm_device *dev,
list_add_tail(&msm_obj->mm_list, &priv->inactive_willneed);
mutex_unlock(&priv->mm_lock);

+ mutex_lock(&priv->obj_lock);
+ list_add_tail(&msm_obj->node, &priv->objects);
+ mutex_unlock(&priv->obj_lock);
+
return obj;

fail:
@@ -1240,6 +1248,10 @@ struct drm_gem_object *msm_gem_import(struct drm_device *dev,
list_add_tail(&msm_obj->mm_list, &priv->inactive_willneed);
mutex_unlock(&priv->mm_lock);

+ mutex_lock(&priv->obj_lock);
+ list_add_tail(&msm_obj->node, &priv->objects);
+ mutex_unlock(&priv->obj_lock);
+
return obj;

fail:
diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index 13aabfe92dac..e6b28edb1db9 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -60,10 +60,16 @@ struct msm_gem_object {
*/
uint8_t vmap_count;

+ /**
+ * Node in list of all objects (mainly for debugfs, protected by
+ * priv->obj_lock
+ */
+ struct list_head node;
+
/**
* An object is either:
- * inactive - on priv->inactive_dontneed/willneed/purged depending
- * on status
+ * inactive - on priv->inactive_dontneed or priv->inactive_willneed
+ * (depending on purgability status)
* active - on one one of the gpu's active_list.. well, at
* least for now we don't have (I don't think) hw sync between
* 2d and 3d one devices which have both, meaning we need to
--
2.30.2