Messages in this thread |  | | Date | Mon, 18 Nov 2013 12:37:07 -0500 | From | Peter Hurley <> | Subject | Re: [PATCH] tty: Only hangup once |
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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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