From 371c2279aa705c32730e738b3f173fb2e62b33e7 Mon Sep 17 00:00:00 2001 From: Alexandru Moise <00moses.alexander00@gmail.com> Date: Sat, 8 Jul 2017 23:43:52 +0200 Subject: [PATCH] drm: inhibit drm drivers register to uninitialized drm core If the DRM core fails to init for whatever reason, ensure that no driver ever calls drm_dev_register(). This is best done at drm_dev_init() as it covers drivers that call drm_dev_alloc() as well as drivers that prefer to embed struct drm_device into their own device struct and call drm_dev_init() themselves. In my case I had so many dynamic device majors used that the major number for DRM (226) was stolen, causing DRM core init to fail after failing to register a chrdev, and ultimately calling debugfs_remove() on drm_debugfs_root in drm_core_exit(). After drm core failed to init, VGEM was still calling drm_dev_register(), ultimately leading to drm_debugfs_init(), with drm_debugfs_root passed as the root for the new debugfs dir at debugfs_create_dir(). This led to a kernel panic once we were either derefencing root->d_inode while it was NULL or calling root->d_inode->i_op->lookup() while it was NULL in debugfs at inode_lock() or lookup_*(). Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com> Signed-off-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/20170708214352.GA27205@gmail.com --- drivers/gpu/drm/drm_drv.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index 37b8ad3e30d8..2ed2d919beae 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -63,6 +63,15 @@ module_param_named(debug, drm_debug, int, 0600); static DEFINE_SPINLOCK(drm_minor_lock); static struct idr drm_minors_idr; +/* + * If the drm core fails to init for whatever reason, + * we should prevent any drivers from registering with it. + * It's best to check this at drm_dev_init(), as some drivers + * prefer to embed struct drm_device into their own device + * structure and call drm_dev_init() themselves. + */ +static bool drm_core_init_complete = false; + static struct dentry *drm_debugfs_root; #define DRM_PRINTK_FMT "[" DRM_NAME ":%s]%s %pV" @@ -484,6 +493,11 @@ int drm_dev_init(struct drm_device *dev, { int ret; + if (!drm_core_init_complete) { + DRM_ERROR("DRM core is not initialized\n"); + return -ENODEV; + } + kref_init(&dev->ref); dev->dev = parent; dev->driver = driver; @@ -966,6 +980,8 @@ static int __init drm_core_init(void) if (ret < 0) goto error; + drm_core_init_complete = true; + DRM_DEBUG("Initialized\n"); return 0; -- 2.20.1