Nouveau - Oct 2011 - [PATCH] drm: serialize access to debugs_nodes.list

Nouveau, when configured with debugfs, creates debugfs files for every
channel, so structure holding list of files needs to be protected from
simultaneous changes by multiple threads.

Without this patch it's possible to hit kernel oops in
drm_debugfs_remove_files just by running a couple of xterms with
looped glxinfo.

Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
---
 drivers/gpu/drm/drm_debugfs.c |    5 +++++
 include/drm/drmP.h            |    1 +
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 9d2668a..1144fbe 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -120,7 +120,9 @@ int drm_debugfs_create_files(struct drm_info_list *files,
int count,
 		tmp->minor = minor;
 		tmp->dent = ent;
 		tmp->info_ent = &files[i];
+		mutex_lock(&minor->debugfs_nodes.mutex);
 		list_add(&(tmp->list), &(minor->debugfs_nodes.list));
+		mutex_unlock(&minor->debugfs_nodes.mutex);
 	}
 	return 0;
 
@@ -149,6 +151,7 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 	int ret;
 
 	INIT_LIST_HEAD(&minor->debugfs_nodes.list);
+	mutex_init(&minor->debugfs_nodes.mutex);
 	sprintf(name, "%d", minor_id);
 	minor->debugfs_root = debugfs_create_dir(name, root);
 	if (!minor->debugfs_root) {
@@ -194,6 +197,7 @@ int drm_debugfs_remove_files(struct drm_info_list *files,
int count,
 	struct drm_info_node *tmp;
 	int i;
 
+	mutex_lock(&minor->debugfs_nodes.mutex);
 	for (i = 0; i < count; i++) {
 		list_for_each_safe(pos, q, &minor->debugfs_nodes.list) {
 			tmp = list_entry(pos, struct drm_info_node, list);
@@ -204,6 +208,7 @@ int drm_debugfs_remove_files(struct drm_info_list *files,
int count,
 			}
 		}
 	}
+	mutex_unlock(&minor->debugfs_nodes.mutex);
 	return 0;
 }
 EXPORT_SYMBOL(drm_debugfs_remove_files);
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 9b7c2bb..c70c943 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -970,6 +970,7 @@ struct drm_info_list {
  * debugfs node structure. This structure represents a debugfs file.
  */
 struct drm_info_node {
+	struct mutex mutex;
 	struct list_head list;
 	struct drm_minor *minor;
 	struct drm_info_list *info_ent;
-- 
1.7.7

On Sun, Oct 30, 2011 at 11:04:48PM +0100, Marcin Slusarz
wrote:
> Nouveau, when configured with debugfs, creates debugfs files for every
> channel, so structure holding list of files needs to be protected from
> simultaneous changes by multiple threads.
> 
> Without this patch it's possible to hit kernel oops in
> drm_debugfs_remove_files just by running a couple of xterms with
> looped glxinfo.
> 
> Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
> ---
>  drivers/gpu/drm/drm_debugfs.c |    5 +++++
>  include/drm/drmP.h            |    1 +
>  2 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
> index 9d2668a..1144fbe 100644
> --- a/drivers/gpu/drm/drm_debugfs.c
> +++ b/drivers/gpu/drm/drm_debugfs.c
> @@ -120,7 +120,9 @@ int drm_debugfs_create_files(struct drm_info_list
*files, int count,
>  		tmp->minor = minor;
>  		tmp->dent = ent;
>  		tmp->info_ent = &files[i];
> +		mutex_lock(&minor->debugfs_nodes.mutex);
>  		list_add(&(tmp->list), &(minor->debugfs_nodes.list));
> +		mutex_unlock(&minor->debugfs_nodes.mutex);
>  	}
>  	return 0;
>  
> @@ -149,6 +151,7 @@ int drm_debugfs_init(struct drm_minor *minor, int
minor_id,
>  	int ret;
>  
>  	INIT_LIST_HEAD(&minor->debugfs_nodes.list);
> +	mutex_init(&minor->debugfs_nodes.mutex);
>  	sprintf(name, "%d", minor_id);
>  	minor->debugfs_root = debugfs_create_dir(name, root);
>  	if (!minor->debugfs_root) {
> @@ -194,6 +197,7 @@ int drm_debugfs_remove_files(struct drm_info_list
*files, int count,
>  	struct drm_info_node *tmp;
>  	int i;
>  
> +	mutex_lock(&minor->debugfs_nodes.mutex);
>  	for (i = 0; i < count; i++) {
>  		list_for_each_safe(pos, q, &minor->debugfs_nodes.list) {
>  			tmp = list_entry(pos, struct drm_info_node, list);
> @@ -204,6 +208,7 @@ int drm_debugfs_remove_files(struct drm_info_list
*files, int count,
>  			}
>  		}
>  	}
> +	mutex_unlock(&minor->debugfs_nodes.mutex);
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_debugfs_remove_files);
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 9b7c2bb..c70c943 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -970,6 +970,7 @@ struct drm_info_list {
>   * debugfs node structure. This structure represents a debugfs file.
>   */
>  struct drm_info_node {
> +	struct mutex mutex;
>  	struct list_head list;
>  	struct drm_minor *minor;
>  	struct drm_info_list *info_ent;
This is just ugly, you're adding a mutex to every drm_info_node, but only
use the one embedded into the minor. On a quick grep we're only ever using
the list in there, so I suggest to
- replace minor->debugfs_node.list with minor->debugfs_list and kill
  ->debugfs_node
- add the mutex as minor->debugfs_lock
That way it's clear what's going on.

Also, you've forgotten to add the locking to i915/i915_debugfs.c

Yours, Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48