Messages in this thread | | | Date | Mon, 20 Jan 2020 11:31:34 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount |
| |
On 20-01-20, 13:58, chenqiwu wrote: > On Mon, Jan 20, 2020 at 11:02:50AM +0530, Viresh Kumar wrote: > > On 19-01-20, 15:09, qiwuchen55@gmail.com wrote: > > > From: chenqiwu <chenqiwu@xiaomi.com> > > > > > > brcm_avs_cpufreq_get() calls cpufreq_cpu_get() to get the cpufreq policy, > > > meanwhile, it also increments the kobject reference count to mark it busy. > > > However, a corresponding call of cpufreq_cpu_put() is ignored to decrement > > > the kobject reference count back, which may lead to a potential stuck risk > > > that the cpuhp thread deadly waits for dropping of kobject refcount when > > > cpufreq policy free. > > > > > > For fixing this bug, cpufreq_get_policy() is referenced to do a proper > > > cpufreq_cpu_get()/cpufreq_cpu_put() and fill a policy copy for the user. > > > If the policy return NULL, we just return 0 to hit the code path of > > > cpufreq_driver->get. > > > > > > Signed-off-by: chenqiwu <chenqiwu@xiaomi.com> > > > --- > > > drivers/cpufreq/brcmstb-avs-cpufreq.c | 12 ++++++++++-- > > > 1 file changed, 10 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c > > > index 77b0e5d..ee0d404 100644 > > > --- a/drivers/cpufreq/brcmstb-avs-cpufreq.c > > > +++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c > > > @@ -452,8 +452,16 @@ static bool brcm_avs_is_firmware_loaded(struct private_data *priv) > > > > > > static unsigned int brcm_avs_cpufreq_get(unsigned int cpu) > > > { > > > - struct cpufreq_policy *policy = cpufreq_cpu_get(cpu); > > > > Why can't we just add a corresponding cpufreq_cpu_put() instead of all this ? > > > > cpufreq_get_policy() does a proper cpufreq_cpu_get()/cpufreq_cpu_put(), > meanwhile fills a policy copy for the user. It equals to using > cpufreq_cpu_get() and a corresponding cpufreq_cpu_put() around access > to the policy pointer. I think both methods are fine here. > What do you think?
cpufreq_get_policy() does an extra memcpy as well, which isn't required at all in your case.
-- viresh
| |