linux-kernel - Re: [PATCH] tty: Only hangup once

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Message-ID: <20131118134211.17861db3@alan.etchedpixels.co.uk>
Date:	Mon, 18 Nov 2013 13:42:11 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Heorhi Valakhanovich <valahanovich@....by>
Cc:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH] tty: Only hangup once

> After upgrading to kernel 3.12 I noticed one issue with tmux software.
> The easiest way to reproduce will be:
> 1. Start tmux session as root.
> 2. Connect via ssh and use "tmux attach" to attach to the running
> session.
> 3. Kill ssh client.
> 
> You can notice that shell (zsh in my case) and "tmux attach" are still
> remains in process' list. That didn't happen in previous kernels.
> I've tried to bisect this in kernel sources and found commit
> cb50e5235b8ae5aa0fe422eaaa8e444024c5bd98 which contains this exact
> patch. I have not enough experience to investigate more so most likely
> I will not find anything more. But it will be good if someone more
> experienced will have a look at it.

The patch should be reverted. The submission gives no reason that the
patch was required - it just adds code and optimises a path that doesn't
need optimising anyway.

It's theoretically true you only need one hangup, unfortunately however
I think it has to be the *last* hangup not the first or there are races
between the tty code and the process group handling.

Alan
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