One last time (Re: SIGCHLD race *trivial* patch)

Nicolas Williams Nicolas.Williams at
Sat Oct 27 03:36:31 EST 2001

One more time. The SIGCHLD race remains, which means that SSHv2 clients
don't always find out about the exiting of their sessions' lead

See below.

On Thu, Oct 25, 2001 at 09:21:02PM -0400, Nicolas Williams wrote:
> 1. my patch doesn't really fix the race -- signal blocking is needed for
>    that. Sigh.

I take it that the BSD sigvec() interface is to be used?

If so, that'll require a compatibility shim for Solaris (which has a
sigvec in /usr/ucblib/libucb, but which I am not sure is useable w.

> 2. I think the normal expectation is that when there are no more open
>    sessions or channels or children that sshd should exit. The opposite
>    ought to be an option. IMHO

Never mind. It turns out that this should be a client side patch as the
client is told when its sessions end and it knows what channels are

> 3. If sshd is to exit when (no more sessions && no more channels && no
>    more children) then either you must use a select() timeout, at least
>    when (no more sessions && no more channels), or sshd must use the
>    signal-handler-writes-to-a-pipe-whose-read-end-is-selected-for trick,
>    as described in the "SIGCHLD race condition race?" thread by Paul
>    Menage.

If sshd is to inform the client of ended sessions then it must reliably
catch SIGCHLD. That requires blocking.

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