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

[Andrew Morton]

On Sun, 26 Apr 2026 01:17:25 -0700 syzbot <syzbot+7d60b33a8a546263da7c@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    6596a02b2078 Merge tag 'drm-next-2026-04-22' of https://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12483702580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=24c8da4692f901cb
> dashboard link: https://syzkaller.appspot.com/bug?extid=7d60b33a8a546263da7c
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.

argh, that dreaded sentence.

Thanks.

Something's definitely amiss.  This is at least the fifth report of
rcu_read_lock() imbalance post-7.0.  Others:

https://lore.kernel.org/69eab803.a00a0220.17a17.004a.GAE@xxxxxxxxxx
https://lore.kernel.org/69eab803.a00a0220.17a17.004b.GAE@xxxxxxxxxx
https://lore.kernel.org/69eafb0e.a00a0220.9259.0031.GAE@xxxxxxxxxx
https://lore.kernel.org/69ebcbe2.a00a0220.7773.0005.GAE@xxxxxxxxxx

In some cases we released it too often, in other cases we failed to
release it.

The first one is slightly more useful in that it tells us that the
not-released rcu_read_lock() was taken in folio_lruvec_lock_irqsave().

Muchun & Qi: you played with that rcu locking in 31b54a5e8916.  Can you
please double-check that we didn't miss something?