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

[Andrew Morton]

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/

> >>
> >>> 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.

> >  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.