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Date: Sat, 20 Sep 2014 22:30:24 +0200 From: Frederic Weisbecker <fweisbec@...il.com> To: LKML <linux-kernel@...r.kernel.org> Cc: Frederic Weisbecker <fweisbec@...il.com>, Peter Zijlstra <peterz@...radead.org>, Dave Jones <davej@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Russell King <linux@....linux.org.uk>, Catalin Iacob <iacobcatalin@...il.com>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Will Deacon <will.deacon@....com>, Ingo Molnar <mingo@...nel.org>, Catalin Marinas <catalin.marinas@....com> Subject: [PATCH 8/8] nohz: nohz full depends on irq work self IPI support The nohz full functionality depends on IRQ work to trigger its own interrupts. As it's used to restart the tick, we can't rely on the tick fallback for irq work callbacks, ie: we can't use the tick to restart the tick itself. Lets reject the full dynticks initialization if that arch support isn't available. As a side effect, this makes sure that nohz kick is never called from the tick. That otherwise would result in illegal hrtimer self-cancellation and lockup. Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org> Cc: Ingo Molnar <mingo@...nel.org> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> --- kernel/time/tick-sched.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index eb4af01..5a9ff24 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -365,6 +365,20 @@ void __init tick_nohz_init(void) return; } + /* + * Full dynticks uses irq work to drive the tick rescheduling on safe + * locking contexts. But then we need irq work to raise its own + * interrupts to avoid circular dependency on the tick + */ + if (!arch_irq_work_has_interrupt()) { + pr_warning("NO_HZ: Can't run full dynticks because arch doesn't " + "support irq work self-IPIs\n"); + cpumask_clear(tick_nohz_full_mask); + cpumask_copy(housekeeping_mask, cpu_possible_mask); + tick_nohz_full_running = false; + return; + } + cpu = smp_processor_id(); if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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