From fba9573b33f8bddd772195c202f6b8ec0751cedd Mon Sep 17 00:00:00 2001 From: Pan Xinhui Date: Thu, 30 Jul 2015 18:10:40 +0800 Subject: [PATCH] cpufreq: Correct a freq check in cpufreq_set_policy() This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ] return error when failing to set minfreq").It attempt to return an error on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq Actually we just need check if new_policy->min > new_policy->max. Because at least one of max/min is copied from cpufreq_get_policy(). For example, when we echo xxx > .../scaling_min_freq, new_policy is copied from policy in cpufreq_get_policy. new_policy->max is same with policy->max. new_policy->min is set to a new value. Let me explain it in deduction method, first statement in if (): new_policy->min > policy->max policy->max == new_policy->max ==> new_policy->min > new_policy->max second statement in if(): new_policy->max < policy->min policy->max < policy->min ==>new_policy->min > new_policy->max (induction method) So we have proved that we only need check if new_policy->min > new_policy->max. After apply this patch, we can also modify ->min and ->max at same time if new freq range is very much different from current freq range. For example, if current freq range is 480000-960000, then we want to set this range to 1120000-2240000, we would fail in the past because new_policy->min > policy->max. As long as the cpufreq range is valid, we has no reason to reject the user. So correct the check to avoid such case. Signed-off-by: Pan Xinhui Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/cpufreq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 0f4e96ff99e8..76a26609d96b 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2190,7 +2190,11 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo)); - if (new_policy->min > policy->max || new_policy->max < policy->min) + /* + * This check works well when we store new min/max freq attributes, + * because new_policy is a copy of policy with one field updated. + */ + if (new_policy->min > new_policy->max) return -EINVAL; /* verify the cpu speed can be set within this limit */ -- 2.30.2