On Thu, Jun 27, 2013 at 12:32:36PM +0530, Viresh Kumar wrote: > On 26 June 2013 23:27, Jacob Shin <[email protected]> wrote: > > On Wed, Jun 26, 2013 at 08:02:29PM +0530, Viresh Kumar wrote: > >> On 26 June 2013 19:58, Jacob Shin <[email protected]> wrote: > >> > On Wed, Jun 26, 2013 at 12:18:27PM +0530, Viresh Kumar wrote: > >> > >> >> I am not sure if this is enough. What if we had ondemand as the > >> >> governor initially, then we changed it to something else. Now also > >> >> cur_policy contains a address and isn't zero. > > > > I just tested this case with this patch applied, and did not have any > > problems. > > Try this: > - you need a system with multiple policy groups to test it > - Suppose we have two groups of CPUs: 0 and 1 > - Set ondemand as governor for both > - change governor of group 1 to something else (we still have valid policy > struct in Ondemand) > - offline all CPUs from group 1. this will free struct cpufreq_policy > - Online these CPUs back, this will reallocate policy > - Now run this function, the earlier policy struct is already freed and > you are accessing it here.
Ah, I understand now. > > >> >> > cpumask_or(&done, &done, policy->cpus); > >> >> > + > >> >> > + if (policy->governor != &cpufreq_gov_ondemand) > >> >> > + continue; > >> > > >> > This should catch that case no ? > >> > >> Policy might be freed and reallocated by then. And so doing > >> policy->governor is dangerous. > > > > Are you worried that after we have passed the above if check, and > > before we access ->tuner governor change might occur? > > > > Is there something synonymous to get/put_online_cpus() for cpufreq to > > prevent governor change while we update ->tuner values? > > > > Otherwise, should just spinlock? > > No, i wasn't worrying about this but a sequence of events that I told to > you earlier. > > Replying to your other mail: > > Hm . any hints on how to check for if ondemand is running on this CPU > > or not ? I'm not sure what the best way to handle this is .. > > Make cur_policy zero in cpufreq_governor_dbs() for > CPUFREQ_GOV_STOP notification. This will make sure we use correct > policy pointer. Thanks for the tip :-) Here is V2: ---8<--- >From d99ee318c0f9c415a60e6b0b79605232edbb749c Mon Sep 17 00:00:00 2001 From: Jacob Shin <[email protected]> Date: Thu, 27 Jun 2013 09:39:48 -0500 Subject: [PATCH V2 1/1] cpufreq: fix NULL pointer deference at od_set_powersave_bias() When initializing the default powersave_bias value, we need to first make sure that this policy is running the ondemand governor. Reported-by: Tim Gardner <[email protected]> Signed-off-by: Jacob Shin <[email protected]> --- drivers/cpufreq/cpufreq_governor.c | 1 + drivers/cpufreq/cpufreq_ondemand.c | 17 +++++++++++++---- 2 files changed, 14 insertions(+), 4 deletions(-) diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index dc9b72e..834ad86 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -403,6 +403,7 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, gov_cancel_work(dbs_data, policy); mutex_lock(&dbs_data->mutex); + cpu_cdbs->cur_policy = NULL; mutex_destroy(&cpu_cdbs->timer_mutex); mutex_unlock(&dbs_data->mutex); diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index 4b9bb5d..93eb5cb 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -47,6 +47,8 @@ static struct od_ops od_ops; static struct cpufreq_governor cpufreq_gov_ondemand; #endif +static unsigned int default_powersave_bias; + static void ondemand_powersave_bias_init_cpu(int cpu) { struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu); @@ -543,7 +545,7 @@ static int od_init(struct dbs_data *dbs_data) tuners->sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR; tuners->ignore_nice = 0; - tuners->powersave_bias = 0; + tuners->powersave_bias = default_powersave_bias; tuners->io_is_busy = should_io_be_busy(); dbs_data->tuners = tuners; @@ -585,6 +587,7 @@ static void od_set_powersave_bias(unsigned int powersave_bias) unsigned int cpu; cpumask_t done; + default_powersave_bias = powersave_bias; cpumask_clear(&done); get_online_cpus(); @@ -593,11 +596,17 @@ static void od_set_powersave_bias(unsigned int powersave_bias) continue; policy = per_cpu(od_cpu_dbs_info, cpu).cdbs.cur_policy; - dbs_data = policy->governor_data; - od_tuners = dbs_data->tuners; - od_tuners->powersave_bias = powersave_bias; + if (!policy) + continue; cpumask_or(&done, &done, policy->cpus); + + if (policy->governor != &cpufreq_gov_ondemand) + continue; + + dbs_data = policy->governor_data; + od_tuners = dbs_data->tuners; + od_tuners->powersave_bias = default_powersave_bias; } put_online_cpus(); } -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
