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Date:   Wed, 30 Aug 2017 19:55:35 +0200
From:   Mike Galbraith <efault@....de>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        "Reshetova, Elena" <elena.reshetova@...el.com>
Subject: Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm:
 Implement fast refcount overflow protection

On Wed, 2017-08-30 at 10:32 -0700, Kees Cook wrote:
> On Wed, Aug 30, 2017 at 10:13 AM, Mike Galbraith <efault@....de> wrote:
> > On Wed, 2017-08-30 at 09:35 -0700, Kees Cook wrote:
> >> On Tue, Aug 29, 2017 at 10:02 PM, Mike Galbraith <efault@....de> wrote:
> >> > On Tue, 2017-08-29 at 11:41 -0700, Kees Cook wrote:
> >> >> Can you also test with 14afee4b6092 ("net: convert sock.sk_wmem_alloc
> >> >> from atomic_t to refcount_t") reverted (instead of ARCH_HAS_REFCOUNT
> >> >> disabled)?
> >> >
> >> > Nogo.
> >>
> >> Thanks for checking!
> >>
> >> > [   44.901930] WARNING: CPU: 5 PID: 0 at net/netlink/af_netlink.c:374 netlink_sock_destruct+0x82/0xa0
> >>
> >> This is so odd if 14afee4b6092 is reverted. What is line 374 for you
> >> in net/netlink/af_netlink.c?
> >
> > 374         WARN_ON(atomic_read(&sk->sk_rmem_alloc));
> >
> > That line is unchanged by 14afee4b6092.
> 
> Uuuuhmm. Wow, now I'm really baffled. I thought you were getting the
> warn from the next line with the refcount usage... I will keep
> digging. Thanks!

I just double checked freshly pulled tip (rapidly moving target), and
it's definitely nogo with CONFIG_ARCH_HAS_REFCOUNT=y and 14afee4b6092
reverted.

	-Mike

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