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.
>
> 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?
-Daniel
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> lib/igt_aux.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/lib/igt_aux.c b/lib/igt_aux.c
> index 4d08d68..f6b5792 100644
> --- a/lib/igt_aux.c
> +++ b/lib/igt_aux.c
> @@ -79,7 +79,7 @@ static void __attribute__((noreturn)) signal_helper_process(pid_t pid)
> /* Interrupt the parent process at 500Hz, just to be annoying */
> while (1) {
> usleep(1000 * 1000 / 500);
> - if (kill(pid, SIGUSR1)) /* Parent has died, so must we. */
> + if (kill(pid, SIGCONT)) /* Parent has died, so must we. */
> exit(0);
> }
> }
> @@ -93,7 +93,7 @@ static void sig_handler(int i)
> * igt_fork_signal_helper:
> *
> * Fork a child process using #igt_fork_helper to interrupt the parent process
> - * with a SIGUSR1 signal at regular quick intervals. The corresponding dummy
> + * with a SIGCONT signal at regular quick intervals. The corresponding dummy
> * signal handler is installed in the parent process.
> *
> * This is useful to exercise ioctl error paths, at least where those can be
> @@ -108,10 +108,12 @@ void igt_fork_signal_helper(void)
> if (igt_only_list_subtests())
> return;
>
> - signal(SIGUSR1, sig_handler);
> + signal(SIGCONT, sig_handler);
> + setpgrp(); /* define a new process group for ourselves */
>
> igt_fork_helper(&signal_helper) {
> - signal_helper_process(getppid());
> + signal(SIGCONT, SIG_IGN);
> + signal_helper_process(-getppid());
> }
> }
>
> --
> 2.7.0.rc3
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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