Received-SPF: pass (google.com: domain of linux-wireless-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <ed2b00dfda5b6ce46a2c2a33093ee56f77af6a8f.camel@sipsolutions.net>
Subject: Re: WARNING in hwsim_new_radio_nl
From:   Johannes Berg <johannes@sipsolutions.net>
To:     syzbot <syzbot+a4aee3f42d7584d76761@syzkaller.appspotmail.com>,
        davem@davemloft.net, kvalo@codeaurora.org,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        mathew.j.martineau@linux.intel.com, matthieu.baerts@tessares.net,
        netdev@vger.kernel.org, pabeni@redhat.com,
        syzkaller-bugs@googlegroups.com
Date:   Tue, 14 Apr 2020 12:38:22 +0200
In-Reply-To: <000000000000cb517b05a32c917b@google.com> (sfid-20200413_160506_506947_12BA215F)
References: <000000000000cb517b05a32c917b@google.com>
         (sfid-20200413_160506_506947_12BA215F)
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

Hi syzbot keepers,

On Mon, 2020-04-13 at 07:05 -0700, syzbot wrote:
> syzbot has bisected this bug to:
> 
> commit 01cacb00b35cb62b139f07d5f84bcf0eeda8eff6
> Author: Paolo Abeni <pabeni@redhat.com>
> Date:   Fri Mar 27 21:48:51 2020 +0000
> 
>     mptcp: add netlink-based PM
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10225bb3e00000

This is, fairly obviously, incorrect. Same with the bisection for
6693adf1698864d21734, which is really the same underlying problem as
this one (though at a different code site).

However, it stands out that this was bisected to a commit that adds a
new generic netlink family in both cases.

This makes sense - the reproducer identifies the family by *number*, but
that number isn't stable, generic netlink families should be identified
by *name*.

Perhaps somehow syzbot could be taught that, so that the bisection is
stable across kernels with different generic netlink families
registered?

Alternatively, we _could_ add some kind of stable ID mode, but I'm not
sure we really want to ... since that would mean people start hardcoding
IDs?

johannes