linux-kernel - Re: [syzbot] [reiserfs?] INFO: task hung in flush_old

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Date:   Wed, 24 May 2023 17:57:13 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        reiserfs-devel@...r.kernel.org, roberto.sassu@...wei.com,
        syzkaller-bugs@...glegroups.com,
        syzbot <syzbot+0a684c061589dcc30e51@...kaller.appspotmail.com>
Subject: Re: [syzbot] [reiserfs?] INFO: task hung in flush_old_commits

On Wed, May 24, 2023 at 11:50 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
> On Wed, 2023-05-24 at 11:11 -0400, Paul Moore wrote:
> > On Wed, May 24, 2023 at 5:59 AM syzbot
> > <syzbot+0a684c061589dcc30e51@...kaller.appspotmail.com> wrote:
> > > syzbot has bisected this issue to:
> > >
> > > commit d82dcd9e21b77d338dc4875f3d4111f0db314a7c
> > > Author: Roberto Sassu <roberto.sassu@...wei.com>
> > > Date:   Fri Mar 31 12:32:18 2023 +0000
> > >
> > >     reiserfs: Add security prefix to xattr name in reiserfs_security_write()
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11c39639280000
> > > start commit:   421ca22e3138 Merge tag 'nfs-for-6.4-2' of git://git.linux-..
> > > git tree:       upstream
> > > final oops:     https://syzkaller.appspot.com/x/report.txt?x=13c39639280000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15c39639280000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=7d8067683055e3f5
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=0a684c061589dcc30e51
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14312791280000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12da8605280000
> > >
> > > Reported-by: syzbot+0a684c061589dcc30e51@...kaller.appspotmail.com
> > > Fixes: d82dcd9e21b7 ("reiserfs: Add security prefix to xattr name in reiserfs_security_write()")
> > >
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> > Roberto, I think we need to resolve this somehow.  As I mentioned
> > earlier, I don't believe this to be a fault in your patch, rather that
> > patch simply triggered a situation that had not been present before,
> > likely because the reiserfs code always failed when writing LSM
> > xattrs.  Regardless, we still need to fix the deadlocks that sysbot
> > has been reporting.
>
> Hi Paul
>
> ok, I will try.

Thanks Roberto.  If it gets to be too challenging, let us know and we
can look into safely disabling the LSM xattrs for reiserfs, I'll be
shocked if anyone is successfully using LSM xattrs on reiserfs.

> > Has anyone dug into the reiserfs code to try and resolve the deadlock?
> >  Considering the state of reiserfs, I'm guessing no one has, and I
> > can't blame them; I personally would have a hard time justifying
> > significant time spent on reiserfs at this point.  Unless someone has
> > any better ideas, I'm wondering if we shouldn't just admit defeat with
> > reiserfs and LSM xattrs and disable/remove the reiserfs LSM xattr
> > support?  Given the bug that Roberto was fixing with the patch in
> > question, it's unlikely this was working anyway.

-- 
paul-moore.com