On 7/16/19 4:36 PM, Shakeel Butt wrote:
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.
I'm surprised too. A quick test with drgn shows root memcg is definitely
allocated:
>>> prog['root_mem_cgroup']
*(struct mem_cgroup *)0xffff8902cf058000 = {
[snip]
But, isn't this a bug?
Thanks,
Yang
Yang, can you please send the above change with signed-off and CC to
stable as well?
thanks,
Shakeel
