On Tue, 5 May 2015 12:38:11 -0700 john.hubbard@xxxxxxxxx wrote:
> From: John Hubbard <jhubbard@xxxxxxxxxx>
>
> Commit 8fcf2cc768acd845c1fed837bf9cfe2d7106336d in linux-next
> introduced a regression in some configurations. Specifically,
> with CONFIG_NO_HZ_FULL set, and CONFIG_NO_HZ_FULL_ALL *not* set,
> the kernel will crash in lockup_detector_init(), due to a
> NULL tick_nohz_full_mask pointer.
>
> This is because the above commit uses tick_nohz_full_mask
> (in lockup_detector_init), if CONFIG_NO_HZ_FULL is set, but
> tick_nohz_full_mask only gets allocated if either:
>
> a) CONFIG_NO_HZ_FULL_ALL is set, or
>
> b) Someone passes in nohz_full=<any_value> on the boot
> args line.
>
> To correct this, change lockup_detector_init so that it does
> a runtime check instead of the ifdef check. This fix is
> simpler than my original proposed fix, thanks to Chris Metcalf
> for that.
>
> ...
>
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -920,14 +920,14 @@ void __init lockup_detector_init(void)
> {
> set_sample_period();
>
> -#ifdef CONFIG_NO_HZ_FULL
> - if (!cpumask_empty(tick_nohz_full_mask))
> - pr_info("Disabling watchdog on nohz_full cores by default\n");
> - cpumask_andnot(&watchdog_cpumask, cpu_possible_mask,
> - tick_nohz_full_mask);
> -#else
> - cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
> -#endif
> + if (tick_nohz_full_enabled()) {
> + if (!cpumask_empty(tick_nohz_full_mask))
> + pr_info("Disabling watchdog on nohz_full cores by default\n");
> + cpumask_andnot(&watchdog_cpumask, cpu_possible_mask,
> + tick_nohz_full_mask);
> + }
> + else
> + cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
Breaks x86_64 allmodconfig:
kernel/watchdog.c: In function 'lockup_detector_init':
kernel/watchdog.c:924: error: 'tick_nohz_full_mask' undeclared (first use in this function)
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