linux-kernel - Re: Should parent's WIFSIGNALED(siginfo->si_status) be true EVEN IF the SIGNAL was caught by the child?

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Date:	Sat, 22 Sep 2007 13:18:53 -0700
From:	"John Z. Bohach" <jzb2@...orsyst.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Should parent's WIFSIGNALED(siginfo->si_status) be true EVEN IF the SIGNAL was caught by the child?

On Saturday 22 September 2007 11:49:09 Michael Kerrisk wrote:
> John,
>

...snip...

>
> If the child terminated by calling exit(), regardless of whether it
> was done from inside a signal handler, then WIFEXITED() should test
> true, but WIFSIGNALED() will not.  If you are seeing otherwise, then
> show a *short* program that demonstrates the behavior.  (But it seems
> unlikely that there would be a kernel bug on this point, so do check
> your program carefully!)

Attached is a (somewhat) short program that demonstates the behavior.  I 
simply compile it with 'make sigtest'.

My observed behavior is:

$ ./sigtest
sigtest started
child1 started
child2 started
selecting...
sigCaught: 3366 receieved signal 15
sigtest 3366 exiting
sigChld: 3365 receieved signal 17
sigChld: 3365 child 3366 WIFEXITED with childStat 15
sigChld: 3365 child 3366 WIFSIGNALED with si_status 15
select error: Interrupted system call
selecting...
sigCaught: 3367 receieved signal 15
sigtest 3367 exiting
sigChld: 3365 receieved signal 17
sigChld: 3365 child 3367 WIFEXITED with childStat 15
sigChld: 3365 child 3367 WIFSIGNALED with si_status 15
select error: Interrupted system call
selecting...
sigCaught: 3365 receieved signal 15
sigtest 3365 exiting
$

To get this output, I ran, from another shell, the following sequence:

$ ps -eaf | grep sigtest
zoltan    3365  2307  0 13:04 pts/0    00:00:00 ./sigtest
zoltan    3366  3365 98 13:04 pts/0    00:00:06 ./sigtest
zoltan    3367  3365 98 13:04 pts/0    00:00:06 ./sigtest
$ kill -SIGTERM 3366
$ kill -SIGTERM 3367
$ kill -SIGTERM 3365

That's it.  What I find odd is that the wait_pid() status and the 
si_status are the same for both a WIFEXITED and a WIFSIGNALED, which 
should be impossible, if I read the documentation right.

Thanks for your responses,
John





View attachment "sigtest.c" of type "text/x-csrc" (9802 bytes)