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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 <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/20170708214352.GA27205@gmail.com
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.