[Intel-gfx] [PATCH igt] core/sighelper: Interrupt everyone in the process group

[Chris Wilson]

On Mon, Jan 11, 2016 at 08:57:33AM +0100, Daniel Vetter wrote:
> On Fri, Jan 08, 2016 at 08:44:29AM +0000, Chris Wilson wrote:
> > Some stress tests create both the signal helper and a lot of competing
> > processes. In these tests, the parent is just waiting upon the children,
> > and the intention is not to keep waking up the waiting parent, but to
> > keep interrupting the children (as we hope to trigger races in our
> > kernel code). kill(-pid) sends the signal to all members of the process
> > group, not just the target pid.
> 
> I don't really have any clue about unix pgroups, but the -pid disappeared
> compared to the previous version.

-getppid().

I felt it was clearer to pass along the "negative pid = process group"
after setting up the process group.

> > We also switch from using SIGUSR1 to SIGCONT to paper over a race
> > condition when forking children that saw the default signal action being
> > run (and thus killing the child).
> 
> I thought I fixed that race by first installing the new signal handler,
> then forking. Ok, rechecked and it's the SYS_getpid stuff, so another
> race. Still I thought signal handlers would survive a fork?

So did irc. They didn't appear to as the children would sporadically
die with SIGUSR1.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre