netdev - Re: [PATCH net 1/2] net: bpfilter: restart bpfilter

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Date:   Sun, 16 Dec 2018 14:20:44 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     ap420073@...il.com
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org
Subject: Re: [PATCH net 1/2] net: bpfilter: restart bpfilter_umh when error
 occurred

From: Taehee Yoo <ap420073@...il.com>
Date: Sat, 15 Dec 2018 13:22:39 +0900

> If bpfilter_umh process is killed, shutdown_umh() is executed via __stop_umh().
> because, __kernel_write() or kernel_read() will be failed in
> __bpfilter_process_sockopt() if bpfilter_umh process had killed
> or crashed. then, __bpfilter_process_sockopt() makes error message and
> calls __stop_umh().

Now I understand, thank you.

This is what happens in the second command of your example:

> >    $ iptables -vnL
> >    $ kill -9 <pid of bpfilter_umh>
> >    $ iptables -vnL
> >    [  480.045136] bpfilter: write fail -32

This second iptables command, which fails, triggers the cleanup.

This second iptables command, however, should not fail either.

What should happen is that when bpfilter_umh is killed, the cleanup is
synchronous, and the next iptables command will cleanly restart
bpftiler_umh and the command will succeeed.

Perhaps what should happen is that fork_usermode_blob() somehow
registers a mechanism by which if the the process forked dies
or exits for some reason, an installed callback is invoked to
perform cleanups.

That would solve all of these problems, and all three iptables
commands in your example would succeed.

What do you think?