Messages in this thread | | | Date | Mon, 20 Jan 2020 11:51:26 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH v3] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount |
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On 20-01-20, 14:13, chenqiwu wrote: > On Mon, Jan 20, 2020 at 11:31:34AM +0530, Viresh Kumar wrote: > > 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 > > Huha..Do you worry about the race conditon with cpufreq policy free path?
No. I just worry about an unnecessary memcpy, nothing else.
-- viresh
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