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Re: Patch(?): bash-2.05/jobs.c loses interrupts


From: Adam J. Richter
Subject: Re: Patch(?): bash-2.05/jobs.c loses interrupts
Date: Mon, 30 Apr 2001 15:05:30 -0700

>>      Linux-2.4.4 has a change, for which I must accept blame,
>> where fork() runs the child first, reducing unnecessary copy-on-write
>> page duplications, because the child will usually promptly do an
>> exec().  I understand this is pretty standard in most unixes.
>> 
>>      Peter Osterlund noticed an annoying side effect of this,
>> which I think is a bash bug.  He wrote:
>> 
>> > Another thing is that the bash loop "while true ; do /bin/true ; done" is
>> > not possible to interrupt with ctrl-c.
>> 
>>      I have reproduced this problem on a single CPU system.
>> I also modified my kernel to sometimes run the fork child first
>> and sometimes not.  In that case, that loop would sometimes
>> abort on a control-C and sometimes ignore it, but ignoring it
>> would not make the loop less likely to abort on another control-C.
>> I'm pretty sure the control-C was being delivered only to the child
>> due to a race condition in bash, which may be mandated by posix.

>Did you reconfigure and rebuild bash on your machine running the 2.4
>kernel, or just use a bash binary built on a previous kernel version?

>Bash has an autoconf test that will, if it detects the need to do so,
>force the job control code to synchronize between parent and child
>when setting up the process group for a new pipeline.  It may be the
>case that you have to reconfigure and rebuild bash to enable that code.

>Look for PGRP_PIPE in config.h.

        Rebuilding bash from pristine 2.05 sources under such a kernel
does *not* solve the problem.  PGRP_PIPE is undef'ed in the resulting
config.h.

Adam J. Richter     __     ______________   4880 Stevens Creek Blvd, Suite 104
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