linux-kernel - Re: [syzbot] [bcachefs?] [rcu?] BUG: unable to handle kernel NULL pointer dereference in rcu

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Message-ID: <aEqfySUeBHDbQ-96@pc636>
Date: Thu, 12 Jun 2025 11:37:13 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Aleksandr Nogikh <nogikh@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>,
	syzbot <syzbot+80e5d6f453f14a53383a@...kaller.appspotmail.com>,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	kent.overstreet@...ux.dev, linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paulmck@...nel.org, rcu@...r.kernel.org,
	syzkaller-bugs@...glegroups.com, urezki@...il.com
Subject: Re: [syzbot] [bcachefs?] [rcu?] BUG: unable to handle kernel NULL
 pointer dereference in rcu_core (3)

On Thu, Jun 12, 2025 at 09:42:32AM +0200, Aleksandr Nogikh wrote:
> On Wed, Jun 11, 2025 at 10:58 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > On Wed, Jun 11, 2025 at 12:57:04PM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> > >
> > > Reported-by: syzbot+80e5d6f453f14a53383a@...kaller.appspotmail.com
> > > Tested-by: syzbot+80e5d6f453f14a53383a@...kaller.appspotmail.com
> > >
> > > Tested on:
> > >
> > > commit:         488ef356 KEYS: Invert FINAL_PUT bit
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=129a660c580000
> >
> > Is there a way to see the whole console output? If Ulad's patch fixes
> > the exact issue, we should be able to see a WARN_ON_ONCE() triggered.
> 
> If WARN_ON_ONCE() were triggered, the associated kernel panic output
> would have been at the end of this log.
> 
> >
> > Regards,
> > Boqun
> >
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=713d218acd33d94
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=80e5d6f453f14a53383a
> 
> FWIW the last time the bug was observed on syzbot was 100 days ago, so
> it has likely been fixed since then or has become much harder to
> reproduce.
> 
That is even worse, if it is last for 100 days already.

--
Uladzislau Rezki