linux-kernel - Re: [PATCH v2] kernel/trace: fix watchdog soft lockup

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Message-ID: <20181130101815.75038642@gandalf.local.home>
Date:   Fri, 30 Nov 2018 10:18:15 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     mingo@...hat.com, akpm@...ux-foundation.org, dvyukov@...gle.com,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] kernel/trace: fix watchdog soft lockup

On Fri, 30 Nov 2018 15:56:22 +0100
Anders Roxell <anders.roxell@...aro.org> wrote:

> When building a allmodconfig kernel for arm64 and boot that in qemu,
> CONFIG_FTRACE_STARTUP_TEST gets enabled and that takes time so the
> watchdog expires and prints out a message like this:
> 'watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [swapper/0:1]'
> Depending on what the what test gets called from init_trace_selftests()
> it stays minutes in the loop.
> Rework so that function cond_resched() gets called in the
> init_trace_selftests loop.
> 

This looks fine to me. Should it be marked for stable, and pushed into
this release cycle, or wait till the next merge window?

-- Steve

> Co-developed-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>  kernel/trace/trace.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 5706599ed534..109becbc81ca 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1547,6 +1547,10 @@ static __init int init_trace_selftests(void)
>  	pr_info("Running postponed tracer tests:\n");
>  
>  	list_for_each_entry_safe(p, n, &postponed_selftests, list) {
> +		/* This loop can take minutes when sanitizers are enabled, so
> +		 * lets make sure we allow RCU processing.
> +		 */
> +		cond_resched();
>  		ret = run_tracer_selftest(p->type);
>  		/* If the test fails, then warn and remove from available_tracers */
>  		if (ret < 0) {