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Date: Fri, 18 Nov 2016 08:47:50 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: "Rafael J. Wysocki" <rjw@...ysocki.net> Cc: Linux PM list <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com> Subject: Re: [PATCH] cpufreq: Avoid using inactive policies On 17-11-16, 16:08, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com> > > There are two places in the cpufreq core in which low-level driver > callbacks may be invoked for an inactive cpufreq policy, which isn't > guaranteed to work in general. Both are due to possible races with > CPU offline. > > First, in cpufreq_get(), the policy may become inactive after > the check against policy->cpus in cpufreq_cpu_get() and before > policy->rwsem is acquired, in which case using the policy going > forward may not be correct. > > Second, an analogous situation is possible in cpufreq_update_policy(). > > Avoid using inactive policies by adding policy_is_inactive() checks > to the code in the above places. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com> > --- > drivers/cpufreq/cpufreq.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > Index: linux-pm/drivers/cpufreq/cpufreq.c > =================================================================== > --- linux-pm.orig/drivers/cpufreq/cpufreq.c > +++ linux-pm/drivers/cpufreq/cpufreq.c > @@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp > > if (policy) { > down_read(&policy->rwsem); > - ret_freq = __cpufreq_get(policy); > + > + if (!policy_is_inactive(policy)) > + ret_freq = __cpufreq_get(policy); > + > up_read(&policy->rwsem); > > cpufreq_cpu_put(policy); > @@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c > > down_write(&policy->rwsem); > > + if (policy_is_inactive(policy)) You also need to set some value to 'ret' as it is uninitialized right now. > + goto unlock; > + > pr_debug("updating policy for CPU %u\n", cpu); > memcpy(&new_policy, policy, sizeof(*policy)); > new_policy.min = policy->user_policy.min; -- viresh
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