Re: [syzbot] [mm?] WARNING: bad unlock balance in do_wp_page

[Qi Zheng]

On 4/27/26 6:44 PM, Andrew Morton wrote:
> On Mon, 27 Apr 2026 17:43:38 +0800 Qi Zheng <qi.zheng@xxxxxxxxx> wrote:
>
> > Alright, it seems I have successfully reproduced it:
> > (The reproducer is attached at the bottom of this email.)
>
> That's a lot of code.  Thanks for doing that.  Maybe there's something
> here we can put into selftests/

If we are inclined to drop rebinding, then perhaps it's unnecessary to
add selftest for it. ;)

> > > > > However, in a production environment, this is practically impossible.
> > > >
> > > > Can you expand on this?
> > > >
> > > > sysbot isn't a production environment ;)
> > >
> > > Rebinding only works when the hierarchy is completely empty. This is
> > > generally not the case in a production environment (e.g. when systemd
> > > is used).
> > >
> > > BTW, it seems rebinding is about to be deprecated:
> > >
> > > cgroup1_reconfigure
> > > --> pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
> > >               task_tgid_nr(current), current->comm);
> > >
> > > Also, it appears the current memcg subsystem assumes that
> > > cgroup_subsys_on_dfl(memory_cgrp_subsys) cannot be changed at runtime.
> > > (Please correct me if I missed anything.)
> > >
> > > If we can get a reproducer, we can try the following fix, or simply drop
> > > rebinding altogether?
>
> We'll want something which is applicable to 7.1-rcX please.  Removal of
> rebinding sounds like something we'd address in 7.2 or later.

Got it.

> > >   From 6ae41b91339625dd7bf0f819f775f26e78171a73 Mon Sep 17 00:00:00 2001
> > > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > > Date: Mon, 27 Apr 2026 11:20:21 +0800
> > > Subject: [PATCH] mm: memcontrol: fix rcu unbalance in
> > >    get_non_dying_memcg_end()
> > >
> > > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > > ---
> > >    mm/memcontrol.c | 30 ++++++++++++++++++++----------
> > >    1 file changed, 20 insertions(+), 10 deletions(-)
> >
> > With the above patch applied, the warnings are gone.
> >
> > If no one objects, I'll submit the formal fix. Or should we actually
> > just remove rebinding instead?
>
> I suggest we just fix up current -rc please.

OK, will do.

Thanks,
Qi

>