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Date:   Thu, 28 May 2020 16:59:42 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Hugh Dickins <hughd@google.com>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
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Subject: Re: mm: mkfs.ext4 invoked oom-killer on i386 - pagecache_get_page
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[Sorry for a late reply - was offline for few days]

On Thu 21-05-20 17:58:55, Johannes Weiner wrote:
> On Thu, May 21, 2020 at 01:06:28PM -0700, Hugh Dickins wrote:
[...]
> >From d9e7ed15d1c9248a3fd99e35e82437549154dac7 Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@cmpxchg.org>
> Date: Thu, 21 May 2020 17:44:25 -0400
> Subject: [PATCH] mm: memcontrol: prepare swap controller setup for integration
>  fix
> 
> Fix crash with cgroup_disable=memory:
> 
> > > > > + mkfs -t ext4 /dev/disk/by-id/ata-TOSHIBA_MG04ACA100N_Y8NRK0BPF6XF
> > > > > mke2fs 1.43.8 (1-Jan-2018)
> > > > > Creating filesystem with 244190646 4k blocks and 61054976 inodes
> > > > > Filesystem UUID: 3bb1a285-2cb4-44b4-b6e8-62548f3ac620
> > > > > Superblock backups stored on blocks:
> > > > > 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
> > > > > 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
> > > > > 102400000, 214990848
> > > > > Allocating group tables:    0/7453                           done
> > > > > Writing inode tables:    0/7453                           done
> > > > > Creating journal (262144 blocks): [   35.502102] BUG: kernel NULL
> > > > > pointer dereference, address: 000000c8
> > > > > [   35.508372] #PF: supervisor read access in kernel mode
> > > > > [   35.513506] #PF: error_code(0x0000) - not-present page
> > > > > [   35.518638] *pde = 00000000
> > > > > [   35.521514] Oops: 0000 [#1] SMP
> > > > > [   35.524652] CPU: 0 PID: 145 Comm: kswapd0 Not tainted
> > > > > 5.7.0-rc6-next-20200519+ #1
> > > > > [   35.532121] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> > > > > 2.2 05/23/2018
> > > > > [   35.539507] EIP: mem_cgroup_get_nr_swap_pages+0x28/0x60
> 
> Swap accounting used to be implied-disabled when the cgroup controller
> was disabled. Restore that for the new cgroup_memory_noswap, so that
> we bail out of this function instead of dereferencing a NULL memcg.
> 
> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> Debugged-by: Hugh Dickins <hughd@google.com>
> Debugged-by: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Yes this looks better. I hope to get to your series soon to have the
full picture finally.

> ---
>  mm/memcontrol.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3e000a316b59..e3b785d6e771 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7075,7 +7075,11 @@ static struct cftype memsw_files[] = {
>  
>  static int __init mem_cgroup_swap_init(void)
>  {
> -	if (mem_cgroup_disabled() || cgroup_memory_noswap)
> +	/* No memory control -> no swap control */
> +	if (mem_cgroup_disabled())
> +		cgroup_memory_noswap = true;
> +
> +	if (cgroup_memory_noswap)
>  		return 0;
>  
>  	WARN_ON(cgroup_add_dfl_cftypes(&memory_cgrp_subsys, swap_files));
> -- 
> 2.26.2

-- 
Michal Hocko
SUSE Labs