Commit cafe4074 authored by Shengming Hu's avatar Shengming Hu Committed by Andrew Morton
Browse files

watchdog/softlockup: fix sample ring index wrap in need_counting_irqs() 

cpustat_tail indexes cpustat_util[], which is a NUM_SAMPLE_PERIODS-sized
ring buffer. need_counting_irqs() currently wraps the index using
NUM_HARDIRQ_REPORT, which only happens to match NUM_SAMPLE_PERIODS.

Use NUM_SAMPLE_PERIODS for the wrap to keep the ring math correct even if
the NUM_HARDIRQ_REPORT or  NUM_SAMPLE_PERIODS changes.

Link: https://lkml.kernel.org/r/tencent_7068189CB6D6689EB353F3D17BF5A5311A07@qq.com


Fixes: e9a9292e ("watchdog/softlockup: Report the most frequent interrupts")
Signed-off-by: default avatarShengming Hu <hu.shengming@zte.com.cn>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zhang Run <zhang.run@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9dc05223

kernel/watchdog.c

+1 −1
Original line number Diff line number Diff line
@@ -550,7 +550,7 @@ static bool need_counting_irqs(void) 
	u8 util;

	int tail = __this_cpu_read(cpustat_tail);



	tail = (tail + NUM_HARDIRQ_REPORT - 1) % NUM_HARDIRQ_REPORT;

	tail = (tail + NUM_SAMPLE_PERIODS - 1) % NUM_SAMPLE_PERIODS;

	util = __this_cpu_read(cpustat_util[tail][STATS_HARDIRQ]);

	return util > HARDIRQ_PERCENT_THRESH;

}