On Thu, Apr 26, 2018 at 08:23:19AM -0400, Chunyu Hu wrote: > kmemleak is using kmem_cache to record every pointers returned from kernel mem > allocation activities such as kmem_cache_alloc(). every time an object from > slab allocator is returned, a following new kmemleak object is allocated. > > And when a slab object is freed, then the kmemleak object which contains > the ptr will also be freed. > > and kmemleak scan thread will run in period to scan the kernel data, stack, > and per cpu areas to check that every pointers recorded by kmemleak has at least > one reference in those areas beside the one recorded by kmemleak. If there > is no place in the memory acreas recording the ptr, then it's possible a leak. > > so once a kmemleak object allocation failed, it has to disable itself, otherwise > it would lose track of some object pointers, and become less meaningful to > continue record and scan the kernel memory for the pointers. So disable > it forever. so this is why kmemleak can't tolerate a slab alloc fail (from fault injection) > > @Catalin, > > Is this right? If something not so correct or precise, please correct me. That's a good description, thanks. > I'm thinking about, is it possible that make kmemleak don't disable itself > when fail_page_alloc is enabled? I can't think clearly what would happen > if several memory allocation missed by kmelkeak trace, what's the bad result? Take for example a long linked list. If kmemleak doesn't track an object in such list (because the metadata allocation failed), such list_head is never scanned and the subsequent objects in the list (pointed at by 'next') will be reported as leaks. Kmemleak pretty much becomes unusable with a high number of false positives. -- Catalin
