From: Andreas Gruenbacher <agruenba@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: syzbot <syzbot+3e5130844b0c0e2b4948@syzkaller.appspotmail.com>,
cluster-devel@redhat.com, gfs2@lists.linux.dev,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
postmaster@duagon.onmicrosoft.com, rpeterso@redhat.com,
syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [gfs2?] WARNING: suspicious RCU usage in gfs2_permission
Date: Mon, 30 Oct 2023 22:05:00 +0100 [thread overview]
Message-ID: <CAHc6FU4Zd0szGBzZBx212K4MgjFJAEMwD1jbTraw0ihMG14Z2w@mail.gmail.com> (raw)
In-Reply-To: <20231025032133.GA1247614@ZenIV>
Al,
On Wed, Oct 25, 2023 at 5:29 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Fri, Oct 20, 2023 at 12:10:38AM -0700, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 0abd1557e21c617bd13fc18f7725fc6363c05913
> > Author: Al Viro <viro@zeniv.linux.org.uk>
> > Date: Mon Oct 2 02:33:44 2023 +0000
> >
> > gfs2: fix an oops in gfs2_permission
> >
> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10b21c33680000
> > start commit: 2dac75696c6d Add linux-next specific files for 20231018
> > git tree: linux-next
> > final oops: https://syzkaller.appspot.com/x/report.txt?x=12b21c33680000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14b21c33680000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=6f8545e1ef7a2b66
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3e5130844b0c0e2b4948
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101c8d09680000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11a07475680000
> >
> > Reported-by: syzbot+3e5130844b0c0e2b4948@syzkaller.appspotmail.com
> > Fixes: 0abd1557e21c ("gfs2: fix an oops in gfs2_permission")
> >
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
> Complaints about rcu_dereference() outside of rcu_read_lock().
>
> We could replace that line with
> if (mask & MAY_NOT_BLOCK)
> gl = rcu_dereference(ip->i_gl);
> else
> gl = ip->i_gl;
> or by any equivalent way to tell lockdep it ought to STFU.
the following should do then, right?
gl = rcu_dereference_check(ip->i_gl, !(mask & MAY_NOT_BLOCK));
> BTW, the amount of rcu_dereference_protected(..., true) is somewhat depressing...
>
> Probably need to turn
> ip->i_gl = NULL;
> in the end of gfs2_evict_inode() into rcu_assign_pointer(ip->i_gl, NULL);
That's what commit 0abd1557e21c6 does already so there's nothing to fix, right?
> and transpose it with the previous line -
> gfs2_glock_put_eventually(ip->i_gl);
>
> I don't think it really matters in this case, though - destruction of the object
> it used to point to is delayed in all cases. Matter of taste (and lockdep
> false positives)...
I don't understand. What would lockdep complain about here?
Thanks,
Andreas
prev parent reply other threads:[~2023-10-30 21:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 18:18 [syzbot] [gfs2?] WARNING: suspicious RCU usage in gfs2_permission syzbot
2023-10-18 14:28 ` syzbot
2023-10-20 7:10 ` syzbot
2023-10-25 3:21 ` Al Viro
2023-10-30 21:05 ` Andreas Gruenbacher [this message]
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