On Fri, Oct 20, 2023 at 12:10:38AM -0700, syzbot wrote:
> syzbot has bisected this issue to:
>
> commit 0abd1557e21c617bd13fc18f7725fc6363c05913
> Author: Al Viro <v...@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+3e5130844b0c0e2b4...@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.
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);
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)...
