Messages in this thread | | | Date | Tue, 14 Jul 2015 10:52:35 +0800 | From | Pan Xinhui <> | Subject | Re: [PATCH] acpi-cpufreq: Add a miss ifdef CONFIG_X86_ACPI_CPUFREQ_CPB |
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hi, Rafael, let me do more explanation :)
On 2015年07月14日 10:09, Pan Xinhui wrote: > 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. > According to line 961, the for loop, patch author assume the first *NULL* may be *at any index* of struct freq_attr *acpi_cpufreq_attr[].
But according to line 965, and the comment also says *a terminator behind it*. patch author assume the first *NULL* is *just right before* the second *NULL* which acts as a terminator. The logic is incorrect. :( Why not just + /* there must be two NULL in the end of acpi_cpufreq_attr[] */ + struct freq_attr **iter = &acpi_cpufreq_attr[sizeof(acpi_cpufreq_attr) - 2]; + if (!WARN_ON(iter[0] || iter[1]))
I don't like that codes assume the index of first *NULL*, so maybe removing line 965, the check if iter[1] == NULL, is more correct and beautiful :)
thanks xinhui
> 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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