On 5/26/21 1:48 PM, Greg KH wrote: > On Wed, May 26, 2021 at 01:38:55PM +0200, Vlastimil Babka wrote: >> >> alias_list a single list and both slab_sysfs_init() and slab_debugfs_init() >> flush it. So only the init call that happens to be called first, does actually >> find an unflushed list. I think you >> need to use a separate list for debugfs (simpler) or a shared list with both >> sysfs and debugfs processing (probably more complicated). >> >> And finally a question, perhaps also for Greg. With sysfs, we hand out the >> lifecycle of struct kmem_cache to sysfs, to ensure we are not reading sysfs >> files of a cache that has been removed. >> >> But with debugfs, what are the guarantees that things won't blow up when a >> debugfs file is being read while somebody calls kmem_cache_destroy() on the cache? > > It's much harder, but usually the default debugfs_file_create() will > handle this for you. See the debugfs_file_create_unsafe() for the > "other" variant where you know you can tear things down "safely". Right, so IIUC debugfs will guarantee that while somebody reads the files, the debugfs cleanup will block, as debugfs_file_get() comment explains. In that case I think we have the cleanup order wrong in this patch: shutdown_cache() should first do debugfs_slab_release() (which would block) and only then proceed with slab_kmem_cache_release() which destroys the fundamental structures such as kmem_cache_node, which are also accessed by the debugfs file handlers. > That being said, yes there are still issues in this area, be careful > about what tools you expect to be constantly hitting debugfs files. FWIW, the files are accessible only to root. > thanks, > > greg k-h >
