Commit 01b4c399 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney
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nohz: Add TICK_DEP_BIT_RCU 



If a nohz_full CPU is looping in the kernel, the scheduling-clock tick
might nevertheless remain disabled.  In !PREEMPT kernels, this can
prevent RCU's attempts to enlist the aid of that CPU's executions of
cond_resched(), which can in turn result in an arbitrarily delayed grace
period and thus an OOM.  RCU therefore needs a way to enable a holdout
nohz_full CPU's scheduler-clock interrupt.

This commit therefore provides a new TICK_DEP_BIT_RCU value which RCU can
pass to tick_dep_set_cpu() and friends to force on the scheduler-clock
interrupt for a specified CPU or task.  In some cases, rcutorture needs
to turn on the scheduler-clock tick, so this commit also exports the
relevant symbols to GPL-licensed modules.

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 54ecb8f7

include/linux/tick.h

+6 −1
Original line number Diff line number Diff line
@@ -108,7 +108,8 @@ enum tick_dep_bits { 
	TICK_DEP_BIT_POSIX_TIMER	= 0,

	TICK_DEP_BIT_PERF_EVENTS	= 1,

	TICK_DEP_BIT_SCHED		= 2,

	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3

	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3,

	TICK_DEP_BIT_RCU		= 4

};



#define TICK_DEP_MASK_NONE		0
@@ -116,6 +117,7 @@ enum tick_dep_bits { 
#define TICK_DEP_MASK_PERF_EVENTS	(1 << TICK_DEP_BIT_PERF_EVENTS)

#define TICK_DEP_MASK_SCHED		(1 << TICK_DEP_BIT_SCHED)

#define TICK_DEP_MASK_CLOCK_UNSTABLE	(1 << TICK_DEP_BIT_CLOCK_UNSTABLE)

#define TICK_DEP_MASK_RCU		(1 << TICK_DEP_BIT_RCU)



#ifdef CONFIG_NO_HZ_COMMON

extern bool tick_nohz_enabled;
@@ -268,6 +270,9 @@ static inline bool tick_nohz_full_enabled(void) { return false; } 
static inline bool tick_nohz_full_cpu(int cpu) { return false; }

static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }



static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }

static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }



static inline void tick_dep_set(enum tick_dep_bits bit) { }

static inline void tick_dep_clear(enum tick_dep_bits bit) { }

static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }

include/trace/events/timer.h

+2 −1
Original line number Diff line number Diff line
@@ -367,7 +367,8 @@ TRACE_EVENT(itimer_expire, 
		tick_dep_name(POSIX_TIMER)		\

		tick_dep_name(PERF_EVENTS)		\

		tick_dep_name(SCHED)			\

		tick_dep_name_end(CLOCK_UNSTABLE)

		tick_dep_name(CLOCK_UNSTABLE)		\

		tick_dep_name_end(RCU)



#undef tick_dep_name

#undef tick_dep_mask_name

kernel/time/tick-sched.c

+7 −0
Original line number Diff line number Diff line
@@ -198,6 +198,11 @@ static bool check_tick_dependency(atomic_t *dep) 
		return true;

	}



	if (val & TICK_DEP_MASK_RCU) {

		trace_tick_stop(0, TICK_DEP_MASK_RCU);

		return true;

	}



	return false;

}
@@ -324,6 +329,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) 
		preempt_enable();

	}

}

EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);



void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)

{
@@ -331,6 +337,7 @@ void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) 


	atomic_andnot(BIT(bit), &ts->tick_dep_mask);

}

EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);



/*

 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse

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