On Mon, Jan 27, 2020 at 09:34:33AM -0800, Roman Gushchin wrote: > Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio > the space for task stacks can be allocated using __vmalloc_node_range(), > alloc_pages_node() and kmem_cache_alloc_node(). In the first and the > second cases page->mem_cgroup pointer is set, but in the third it's > not: memcg membership of a slab page should be determined using the > memcg_from_slab_page() function, which looks at > page->slab_cache->memcg_params.memcg . In this case, using > mod_memcg_page_state() (as in account_kernel_stack()) is incorrect: > page->mem_cgroup pointer is NULL even for pages charged to a non-root > memory cgroup. > > In order to fix it, let's introduce a mod_memcg_obj_state() helper, > which takes a pointer to a kernel object as a first argument, uses > mem_cgroup_from_obj() to get a RCU-protected memcg pointer and > calls mod_memcg_state(). It allows to handle all possible > configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE > values) without spilling any memcg/kmem specifics into fork.c . The change looks good to me, but it sounds like this is a bug with actual consequences to userspace. Can you elaborate on that in the changelog please? Maybe add a Fixes: line, if applicable?
