On Mon, Sep 22, 2003 at 01:57:58PM -0500, Darin Dugan wrote:
> http://groups.yahoo.com/group/amanda-users/message/46310
> 
> [...] Does anyone else 
> think it odd that deleting that one line cures the warning without causing 
> any problems?

Not at all.  As the referenced message says, amdump is doing
something whose effects are undefined.  The patch makes it not do
that.

In case you're interested "wait()" says to wait until one of the
caller's child processes exits, and then return the child's exit
status to the caller (in this case, the caller is amdump).

"signal(SIGCHLD, SIG_IGN)" says ... well, I won't go into what
its main purpose is, since that would take explaining all about
signals.  But as a side-effect, it says, "don't keep around the
child-process information necessary to satisfy wait() calls".  In
fact, I think this side-effect is system-dependent.

So amdump is asking the kernel to do contradictory things: first,
"forget about my child processes; I won't be asking about them",
then "tell me about my child processes".  The patch simply makes
it not make the first request; thus the second request is no
longer a problem.

> I'm wondering if anyone has done a kernel upgrade to 2.4.20-20.9 (RH9.0) 
> as mentioned that
> it fixes signal delivery race condition, as I don't know whether to 
> follow the Amanda patch, or
> the kernel patch.

There's no reason to assume they're mutually exclusive!

The Amanda patch can't hurt, so do that for sure.  I don't know
about the kernel patch one way or the other.

--

|  | /\
|-_|/  >   Eric Siegerman, Toronto, Ont.        erics AT telepres DOT com
|  |  /
When I came back around from the dark side, there in front of me would
be the landing area where the crew was, and the Earth, all in the view
of my window. I couldn't help but think that there in front of me was
all of humanity, except me.
        - Michael Collins, Apollo 11 Command Module Pilot