Re: memcg oops: memcg_kmem_charge_memcg()->try_charge()->page_counter_try_charge()->BOOM

[Roman Gushchin]

On Mon, Oct 29, 2018 at 05:35:38PM +0100, Mike Galbraith wrote:
> On Mon, 2018-10-29 at 14:20 +0100, Michal Hocko wrote:
> > 
> > > [    4.420976] Code: f3 c3 0f 1f 00 0f 1f 44 00 00 48 85 ff 0f 84 a8 00 00 00 41 56 48 89 f8 41 55 49 89 fe 41 54 49 89 d5 55 49 89 f4 53 48 89 f3 <f0> 48 0f c1 1f 48 01 f3 48 39 5f 18 48 89 fd 73 17 eb 41 48 89 e8
> > > [    4.424162] RSP: 0018:ffffb27840c57cb0 EFLAGS: 00010202
> > > [    4.425236] RAX: 00000000000000f8 RBX: 0000000000000020 RCX: 0000000000000200
> > > [    4.426467] RDX: ffffb27840c57d08 RSI: 0000000000000020 RDI: 00000000000000f8
> > > [    4.427652] RBP: 0000000000000001 R08: 0000000000000000 R09: ffffb278410bc000
> > > [    4.428883] R10: ffffb27840c57ed0 R11: 0000000000000040 R12: 0000000000000020
> > > [    4.430168] R13: ffffb27840c57d08 R14: 00000000000000f8 R15: 00000000006000c0
> > > [    4.431411] FS:  00007f79081a3940(0000) GS:ffff92a4b7bc0000(0000) knlGS:0000000000000000
> > > [    4.432748] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [    4.433836] CR2: 00000000000000f8 CR3: 00000002310ac002 CR4: 00000000001606e0
> > > [    4.435500] Call Trace:
> > > [    4.436319]  try_charge+0x92/0x7b0
> > > [    4.437284]  ? unlazy_walk+0x4c/0xb0
> > > [    4.438676]  ? terminate_walk+0x91/0x100
> > > [    4.439984]  memcg_kmem_charge_memcg+0x28/0x80
> > > [    4.441059]  memcg_kmem_charge+0x88/0x1d0
> > > [    4.442105]  copy_process.part.37+0x23a/0x2070
> > 
> > Could you faddr2line this please?
> 
> homer:/usr/local/src/kernel/linux-master # ./scripts/faddr2line vmlinux copy_process.part.37+0x23a
> copy_process.part.37+0x23a/0x2070:
> memcg_charge_kernel_stack at kernel/fork.c:401
> (inlined by) dup_task_struct at kernel/fork.c:850
> (inlined by) copy_process at kernel/fork.c:1750
> 
> I bisected it this afternoon, and confirmed the result via revert.
> 
> 9b6f7e163cd0f468d1b9696b785659d3c27c8667 is the first bad commit
> commit 9b6f7e163cd0f468d1b9696b785659d3c27c8667
> Author: Roman Gushchin <guro@xxxxxx>
> Date:   Fri Oct 26 15:03:19 2018 -0700
> 
>     mm: rework memcg kernel stack accounting


Hi Mike!

Thank you for the report!

Do you see it reliable every time you boot up the machine?
How do you run kvm? Is there something special about your cgroup setup?

I've made several attempts to reproduce the issue, but haven't got anything
so far. I've used your config, and played with different cgroups setups.

Do you know where in the page_counter_try_charge() it fails?

Also, can you, please, check if the following patch mitigates the problem?

Thanks!

--

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 54920cbc46bf..a7d6e95450f8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2597,6 +2597,9 @@ int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
                return 0;
 
        memcg = get_mem_cgroup_from_current();
+       if (!memcg)
+               return 0;
+
        if (!mem_cgroup_is_root(memcg)) {
                ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
                if (!ret)