linux-kernel - Re: [PATCH 1/8] perf: Allow to block process in syscall tracepoints

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Message-ID: <20181206081028.GE4234@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Dec 2018 09:10:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Luis Claudio R. Goncalves" <lclaudio@...g.org>, ldv@...linux.org,
        esyr@...hat.com, Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/8] perf: Allow to block process in syscall tracepoints

On Wed, Dec 05, 2018 at 05:05:02PM +0100, Jiri Olsa wrote:
> +static void trace_block_syscall(struct pt_regs *regs, bool enter)
> +{
> +	current->perf_blocked = true;
> +
> +	do {
> +		schedule_timeout(100 * HZ);
> +		current->perf_blocked_cnt = 0;
> +
> +		if (enter) {
> +			/* perf syscalls:* enter */
> +			perf_trace_syscall_enter(regs);
> +
> +			/* perf raw_syscalls:* enter */
> +			perf_trace_sys_enter(&event_sys_enter, regs, regs->orig_ax);
> +		} else {
> +			/* perf syscalls:* enter */
> +			perf_trace_syscall_exit(regs);
> +
> +			/* perf raw_syscalls:* enter */
> +			perf_trace_sys_exit(&event_sys_exit, regs, regs->ax);
> +		}
> +	} while (current->perf_blocked_cnt);
> +
> +	current->perf_blocked = false;
> +}

I don't understand this.. why are we using schedule_timeout() and all
that?