Messages in this thread | | | Date | Tue, 14 Jul 2015 10:09:47 +0800 | From | Pan Xinhui <> | Subject | Re: [PATCH] acpi-cpufreq: Add a miss ifdef CONFIG_X86_ACPI_CPUFREQ_CPB |
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hi, Rafael, thanks for you reply :) On 2015年07月14日 07:26, Rafael J. Wysocki wrote: > On Monday, July 13, 2015 02:33:08 PM Pan Xinhui wrote: >> hi, Rafeal >> thanks for your reply. :) >> >> On 2015年07月11日 04:44, Rafael J. Wysocki wrote: >>> Hi, >>> >>> On Fri, Jul 10, 2015 at 7:50 AM, Pan Xinhui <xinhuix.pan@intel.com> wrote: >>>> >>>> If CONFIG_X86_ACPI_CPUFREQ_CPB has not been defined, the placeholder for >>>> cpb is not needed. Add ifdef around it. >>>> >>>> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com> >>>> --- >>>> drivers/cpufreq/acpi-cpufreq.c | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c >>>> index e7fcaa6..314a19e 100644 >>>> --- a/drivers/cpufreq/acpi-cpufreq.c >>>> +++ b/drivers/cpufreq/acpi-cpufreq.c >>>> @@ -884,7 +884,9 @@ static int acpi_cpufreq_resume(struct cpufreq_policy *policy) >>>> static struct freq_attr *acpi_cpufreq_attr[] = { >>>> &cpufreq_freq_attr_scaling_available_freqs, >>>> &freqdomain_cpus, >>>> +#ifdef CONFIG_X86_ACPI_CPUFREQ_CPB >>>> NULL, /* this is a placeholder for cpb, do not remove */ >>>> +#endif >>> >>> Adding the ifdef here doesn't change anything, because the next NULL >>> will play the role of the one you've just #ifdefed and the structure >>> will be filled with zeros from that point on anyway. >>> >> Yes, adding ifdef here does not change any binary codes. But I want to make the codes more readable. :) >> Patch author has noticed two *NULL* here would confuse people, especially who first read this acpi-cpufreq.c file >> From code style point, it would be better to have #ifdef around it. > > Not really. > > Why don't you simply drop *both* NULLs? > Just like string end with *NULL* :)
1021 static int cpufreq_add_dev_interface(struct cpufreq_policy *policy, 1022 struct device *dev) 1023 { 1024 struct freq_attr **drv_attr; 1025 int ret = 0; 1026 1027 /* set up files for this cpu device */ 1028 drv_attr = cpufreq_driver->attr; 1029 while (drv_attr && *drv_attr) { 1030 ret = sysfs_create_file(&policy->kobj, &((*drv_attr)->attr)); 1031 if (ret) 1032 return ret; 1033 drv_attr++; 1034 } If struct freq_attr *acpi_cpufreq_attr[] did not end with NULL, line 1033 will access invalid data area. If *drv_attr(the data after struct freq_attr * array[]) happened to be not NULL. panic may hit in sysfs_create_file :( So at least one *NULL* must be in the end of freq_attr *array[].
Actually in acpi-cpufreq.c, in acpi_cpufreq_init function. 957 struct freq_attr **iter; 958 959 pr_debug("adding sysfs entry for cpb\n"); 960 961 for (iter = acpi_cpufreq_attr; *iter != NULL; iter++) 962 ; 963 964 /* make sure there is a terminator behind it */ 965 if (iter[1] == NULL) 966 *iter = &cpb; 967 } line965, check of iter[1] is not needed. Maybe the patch author was afraid of an unexpected remove of first *NULL*. It might be a better solution to add ifdef CONFIG_X86_ACPI_CPUFREQ_CPB around that *NULL*, and remove this !iter[1] check.
thanks xinhui
> >> >>> You'd need to #ifdef it in the struct freq_attr definition, but I'm >>> not sure it's worth the effort. >>> >> >> struct freq_attr *cpb* is defined in #ifdef section. :) > > Ah, OK. > >
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