linux-kernel - Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending

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Date: Wed, 13 Mar 2024 15:15:50 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ian Rogers <irogers@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>, Marco Elver <elver@...gle.com>,
	Mark Rutland <mark.rutland@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending_irq() work
 on RT.

On 2024-03-13 10:47:33 [-0300], Arnaldo Carvalho de Melo wrote:
> /* For exec'd child. */
> static void exec_child(void)
> {
>         struct sigaction action = {};
>         const int val = 42;
> 
>         /* Set up sigtrap handler in case we erroneously receive a trap. */
>         action.sa_flags = SA_SIGINFO | SA_NODEFER;
>         action.sa_sigaction = sigtrap_handler;
>         sigemptyset(&action.sa_mask);
>         if (sigaction(SIGTRAP, &action, NULL))
>                 _exit((perror("sigaction failed"), 1));
> 
>         /* Signal parent that we're starting to spin. */
>         if (write(STDOUT_FILENO, &val, sizeof(int)) == -1)
>                 _exit((perror("write failed"), 1));
> 
>         /* Should hang here until killed. */
>         while (!signal_count);
> }
> 
> So probably just a test needing to be a bit more polished?

Maybe. I'm not sure where this is coming from. Either someone should
kill or the signal should be delivered but, hmm… If the signal isn't
coming then it might one of those without a perf counter.

> Seems like it, on a newer machine, faster, I managed to reproduce it on
> a non-RT kernel, with one exec_child remaining:

Okay, so no regression. That is something ;)

> - Arnaldo

Sebastian