core/sighelper: Interrupt everyone in the process group
core/sighelper: Interrupt everyone in the process group

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.

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).

Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>
Acked-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools