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Commit a23314e9 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/cpufreq: Fix 32-bit math overflow 



Vincent Wang reported that get_next_freq() has a mult overflow bug on
32-bit platforms in the IOWAIT boost case, since in that case {util,max}
are in freq units instead of capacity units.

Solve this by moving the IOWAIT boost to capacity units. And since this
means @max is constant; simplify the code.

Reported-by: default avatarVincent Wang <vincent.wang@unisoc.com>
Tested-by: default avatarVincent Wang <vincent.wang@unisoc.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190305083202.GU32494@hirez.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ad01423a

kernel/sched/cpufreq_schedutil.c

+25 −34
Original line number Diff line number Diff line
@@ -48,10 +48,10 @@ struct sugov_cpu { 


	bool			iowait_boost_pending;

	unsigned int		iowait_boost;

	unsigned int		iowait_boost_max;

	u64			last_update;



	unsigned long		bw_dl;

	unsigned long		min;

	unsigned long		max;



	/* The field below is for single-CPU policies only: */
@@ -303,8 +303,7 @@ static bool sugov_iowait_reset(struct sugov_cpu *sg_cpu, u64 time, 
	if (delta_ns <= TICK_NSEC)

		return false;



	sg_cpu->iowait_boost = set_iowait_boost

		? sg_cpu->sg_policy->policy->min : 0;

	sg_cpu->iowait_boost = set_iowait_boost ? sg_cpu->min : 0;

	sg_cpu->iowait_boost_pending = set_iowait_boost;



	return true;
@@ -344,14 +343,13 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, 


	/* Double the boost at each request */

	if (sg_cpu->iowait_boost) {

		sg_cpu->iowait_boost <<= 1;

		if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)

			sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;

		sg_cpu->iowait_boost =

			min_t(unsigned int, sg_cpu->iowait_boost << 1, SCHED_CAPACITY_SCALE);

		return;

	}



	/* First wakeup after IO: start with minimum boost */

	sg_cpu->iowait_boost = sg_cpu->sg_policy->policy->min;

	sg_cpu->iowait_boost = sg_cpu->min;

}



/**
@@ -373,47 +371,38 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, 
 * This mechanism is designed to boost high frequently IO waiting tasks, while

 * being more conservative on tasks which does sporadic IO operations.

 */

static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,

			       unsigned long *util, unsigned long *max)

static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,

					unsigned long util, unsigned long max)

{

	unsigned int boost_util, boost_max;

	unsigned long boost;



	/* No boost currently required */

	if (!sg_cpu->iowait_boost)

		return;

		return util;



	/* Reset boost if the CPU appears to have been idle enough */

	if (sugov_iowait_reset(sg_cpu, time, false))

		return;

		return util;



	if (!sg_cpu->iowait_boost_pending) {

		/*

	 * An IO waiting task has just woken up:

	 * allow to further double the boost value

	 */

	if (sg_cpu->iowait_boost_pending) {

		sg_cpu->iowait_boost_pending = false;

	} else {

		/*

		 * Otherwise: reduce the boost value and disable it when we

		 * reach the minimum.

		 * No boost pending; reduce the boost value.

		 */

		sg_cpu->iowait_boost >>= 1;

		if (sg_cpu->iowait_boost < sg_cpu->sg_policy->policy->min) {

		if (sg_cpu->iowait_boost < sg_cpu->min) {

			sg_cpu->iowait_boost = 0;

			return;

			return util;

		}

	}



	sg_cpu->iowait_boost_pending = false;



	/*

	 * Apply the current boost value: a CPU is boosted only if its current

	 * utilization is smaller then the current IO boost level.

	 * @util is already in capacity scale; convert iowait_boost

	 * into the same scale so we can compare.

	 */

	boost_util = sg_cpu->iowait_boost;

	boost_max = sg_cpu->iowait_boost_max;

	if (*util * boost_max < *max * boost_util) {

		*util = boost_util;

		*max = boost_max;

	}

	boost = (sg_cpu->iowait_boost * max) >> SCHED_CAPACITY_SHIFT;

	return max(boost, util);

}



#ifdef CONFIG_NO_HZ_COMMON
@@ -460,7 +449,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, 


	util = sugov_get_util(sg_cpu);

	max = sg_cpu->max;

	sugov_iowait_apply(sg_cpu, time, &util, &max);

	util = sugov_iowait_apply(sg_cpu, time, util, max);

	next_f = get_next_freq(sg_policy, util, max);

	/*

	 * Do not reduce the frequency if the CPU has not been idle
@@ -500,7 +489,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) 


		j_util = sugov_get_util(j_sg_cpu);

		j_max = j_sg_cpu->max;

		sugov_iowait_apply(j_sg_cpu, time, &j_util, &j_max);

		j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max);



		if (j_util * max > j_max * util) {

			util = j_util;
@@ -837,7 +826,9 @@ static int sugov_start(struct cpufreq_policy *policy) 
		memset(sg_cpu, 0, sizeof(*sg_cpu));

		sg_cpu->cpu			= cpu;

		sg_cpu->sg_policy		= sg_policy;

		sg_cpu->iowait_boost_max	= policy->cpuinfo.max_freq;

		sg_cpu->min			=

			(SCHED_CAPACITY_SCALE * policy->cpuinfo.min_freq) /

			policy->cpuinfo.max_freq;

	}



	for_each_cpu(cpu, policy->cpus) {