linux-kernel - Re: [syzbot] [mm?] [cgroups?] WARNING in __mod_memcg_lruvec

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Date: Mon, 6 May 2024 09:12:53 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: syzbot <syzbot+9319a4268a640e26b72b@...kaller.appspotmail.com>, 
	akpm@...ux-foundation.org, cgroups@...r.kernel.org, hannes@...xchg.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...nel.org, 
	muchun.song@...ux.dev, roman.gushchin@...ux.dev, 
	syzkaller-bugs@...glegroups.com, yuzhao@...gle.com
Subject: Re: [syzbot] [mm?] [cgroups?] WARNING in __mod_memcg_lruvec_state

On Mon, May 6, 2024 at 8:59 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> On Mon, May 06, 2024 at 02:11:57PM +0000, Yosry Ahmed wrote:
> > On Mon, May 06, 2024 at 06:03:29AM -0700, syzbot wrote:
> > > syzbot has found a reproducer for the following issue on:
> > >
> > > HEAD commit:    2b84edefcad1 Add linux-next specific files for 20240506
> > > git tree:       linux-next
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1164931f180000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=b499929e4aaba1af
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=9319a4268a640e26b72b
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=123d5d1f180000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16527450980000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/6a22cf95ee14/disk-2b84edef.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/f5c45b515282/vmlinux-2b84edef.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/9bf98258a662/bzImage-2b84edef.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+9319a4268a640e26b72b@...kaller.appspotmail.com
> > >
> > > ------------[ cut here ]------------
> > > __mod_memcg_lruvec_state: missing stat item 25
> > > WARNING: CPU: 0 PID: 5091 at mm/memcontrol.c:999 __mod_memcg_lruvec_state+0x18c/0x430 mm/memcontrol.c:999
> >
> > This doesn't seem to be the same issue as the original one syzbot
> > reported. It's the same function but a different warning. I am not sure
> > how to tell syzbot that.
> >
> > Anyway, this warning is the one newly introduced by Shakeel. It is
> > firing because NR_SHMEM_PMDMAPPED and/or NR_FILE_PMDMAPPED are being
> > updated using __lruvec_stat_mod_folio(), which also updates the memcg
> > stats. However, these stats are not exported per-memcg.
> >
> > I think the following should fix it.
> >
>
> Hey Yosry, can you please post your patch with the signoff? The patch
> looks good and you can put my ack on it.

Will do. I noticed we also update these stats from
__folio_remove_rmap(). I will send a patch fixing these as well, so
I'll not include your Ack for that as it will be different.