Commit 6b442bc8 authored May 07, 2015 by Thomas Gleixner Committed by Ingo Molnar May 07, 2015

nohz: Fix !HIGH_RES_TIMERS hang



Simon Horman reported this crash on a system with
high-res timers disabled but nohz enabled:

  > ------------[ cut here ]------------
  > kernel BUG at kernel/irq_work.c:135!

    BUG_ON(!irqs_disabled());

So something enabled interrupts in the periodic tick handling machinery,
and that code path indeed has a local_irq_disable()/enable pair in
tick_nohz_switch_to_nohz() which causes havoc. Fix it.

This patch also fixes a +nohz -hrtimers hang reported by Ingo Molnar.

Reported-by: Simon Horman <horms@verge.net.au>
Reported-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: LAK <linux-arm-kernel@lists.infradead.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1505071425520.4225@nanos


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 38d23a6c

kernel/time/tick-sched.c

+3 −6

Original line number	Diff line number	Diff line
		@@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
		if (!tick_nohz_enabled)
		return;

		local_irq_disable();
		if (tick_switch_to_oneshot(tick_nohz_handler)) {
		local_irq_enable();
		if (tick_switch_to_oneshot(tick_nohz_handler))
		return;
		}

		tick_nohz_active = 1;
		ts->nohz_mode = NOHZ_MODE_LOWRES;

		@@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
		hrtimer_forward_now(&ts->sched_timer, tick_period);
		hrtimer_set_expires(&ts->sched_timer, next);
		tick_program_event(next, 1);
		local_irq_enable();
		}

		/*
		@@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
		* Called cyclic from the hrtimer softirq (driven by the timer
		* softirq) allow_nohz signals, that we can switch into low-res nohz
		* mode, because high resolution timers are disabled (either compile
		* or runtime).
		* or runtime). Called with interrupts disabled.
		*/
		int tick_check_oneshot_change(int allow_nohz)
		{

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