Adding related people. The thread starts at: http://lkml.kernel.org/r/1562795006.8510.19.camel@xxxxxx On Mon, Jul 15, 2019 at 8:01 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote: > > > > On 7/15/19 6:36 PM, Qian Cai wrote: > > > >> On Jul 15, 2019, at 8:22 PM, Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote: > >> > >> > >> > >> On 7/15/19 2:23 PM, Qian Cai wrote: > >>> On Fri, 2019-07-12 at 12:12 -0700, Yang Shi wrote: > >>>>> Another possible lead is that without reverting the those commits below, > >>>>> kdump > >>>>> kernel would always also crash in shrink_slab_memcg() at this line, > >>>>> > >>>>> map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, true); > >>>> This looks a little bit weird. It seems nodeinfo[nid] is NULL? I didn't > >>>> think of where nodeinfo was freed but memcg was still online. Maybe a > >>>> check is needed: > >>> Actually, "memcg" is NULL. > >> It sounds weird. shrink_slab() is called in mem_cgroup_iter which does pin the memcg. So, the memcg should not go away. > > Well, the commit “mm: shrinker: make shrinker not depend on memcg kmem” changed this line in shrink_slab_memcg(), > > > > - if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) > > + if (!mem_cgroup_online(memcg)) > > return 0; > > > > Since the kdump kernel has the parameter “cgroup_disable=memory”, shrink_slab_memcg() will no longer be able to handle NULL memcg from mem_cgroup_iter() as, > > > > if (mem_cgroup_disabled()) > > return NULL; > > Aha, yes. memcg_kmem_enabled() implicitly checks !mem_cgroup_disabled(). > Thanks for figuring this out. I think we need add mem_cgroup_dsiabled() > check before calling shrink_slab_memcg() as below: > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a0301ed..2f03c61 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -701,7 +701,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int > nid, > unsigned long ret, freed = 0; > struct shrinker *shrinker; > > - if (!mem_cgroup_is_root(memcg)) > + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) > return shrink_slab_memcg(gfp_mask, nid, memcg, priority); > > if (!down_read_trylock(&shrinker_rwsem)) > We were seeing unneeded oom-kills on kernels with "cgroup_disabled=memory" and Yang's patch series basically expose the bug to crash. I think the commit aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()") missed the case for "cgroup_disabled=memory". However I am surprised that root_mem_cgroup is allocated even for "cgroup_disabled=memory" and it seems like css_alloc() is called even before checking if the corresponding controller is disabled. Yang, can you please send the above change with signed-off and CC to stable as well? thanks, Shakeel
