On 11/18/2013 08:42 AM, One Thousand Gnomes wrote:
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.
Heorhi,
Thanks for the report.
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.
This may have been a bug in previous kernels.
The tmux(1) man page has this to say:
Each session is persistent and will survive accidental disconnection
(such as ssh(1) connection timeout) or intentional detaching (with the
`C-b d' key strokes). tmux may be reattached using:
$ tmux attach
I'll confirm with tmux author(s) what the intended behavior is.
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.
Alan,
This patch isn't about optimizing; it's about guaranteeing the line discipline
and a tty driver that ops->hangup() will only occur once for any given tty.
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.
I doubt this is caused by a race condition; the first hangup would do most
of the destruction regardless, and a second hangup can't really race with
the first because of the tty_lock() held for most of the hangup.
In any event, it's worth discovering what state a subsequent hangup can
effect that the first hangup left incomplete. I'll look into it.
Regards,
Peter Hurley
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