Date: Thu, 13 Nov 1997 15:44:15 -0800 (PST) From: Sean Eric Fagan <sef@kithrup.com> To: hackers@freebsd.org Subject: Re: unkillable process Message-ID: <199711132344.PAA04605@kithrup.com>
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>I wrote:
>> 1. Create a named pipe
>> 2. Start typing into it using cat
>> 3. Hit control-C as many times as you want
>>
>> You'll see that the process will not die even with kill -9,
>> as it is stuck in uninterrupible disk sleep ("fifo").
>
>According to sef, the problem is that the child (csh or tcsh
>but not sh) is ignoring SIGINT, the parent opens the file
>after vfork()'ing, and something else (now I forgot already).
My quick summary (I haven't dived into csh code yet) is that csh (and tcsh)
are doing:
vfork() -- parent sleeps uninterruptably until child exec's or exits
signal(SIGINT, SIG_IGN); -- and other signals, presumably
open("pipe", O_CREAT|O_TRUNC, ...)
At that piont, the child is asleep in fifo_open(). It is interruptable --
but SIGINT is ignored! So are some other signals.
The parent is unkillable; it cannot be made killable, since a vfork'd parent
process is not really there -- the child is really it. (This is a holdover
from the original implementation.)
I think the fix is going to be in csh and tcsh -- I don't think they should
be opening the file in teh child, but should only do it in the parent.
I'm waiting to hear from some other people as well.
Sean.
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