Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753320AbbGRAIN (ORCPT ); Fri, 17 Jul 2015 20:08:13 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:54240 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751725AbbGRAIM convert rfc822-to-8bit (ORCPT ); Fri, 17 Jul 2015 20:08:12 -0400 From: "Rafael J. Wysocki" To: Pan Xinhui Cc: "Rafael J. Wysocki" , Linux Kernel Mailing List , "linux-pm@vger.kernel.org" , Viresh Kumar , "yanmin_zhang@linux.intel.com" , "mnipxh@163.com" Subject: Re: [PATCH] acpi-cpufreq: Add a miss ifdef CONFIG_X86_ACPI_CPUFREQ_CPB Date: Sat, 18 Jul 2015 02:34:52 +0200 Message-ID: <15297094.Px11LlFYVk@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <55A47973.5080900@intel.com> References: <559F5D13.8050104@intel.com> <55A46F6B.6030006@intel.com> <55A47973.5080900@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5390 Lines: 143 On Tuesday, July 14, 2015 10:52:35 AM Pan Xinhui wrote: > 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 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 > >>>>> --- > >>>>> 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[]. OK, so the array is NULL-terminated and one NULL is needed to mark the end of it. > > > > 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. Ah, so that is an exceptionally ugly piece of code. What about the patch below? --- drivers/cpufreq/acpi-cpufreq.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) Index: linux-pm/drivers/cpufreq/acpi-cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/acpi-cpufreq.c +++ linux-pm/drivers/cpufreq/acpi-cpufreq.c @@ -884,7 +884,9 @@ static int acpi_cpufreq_resume(struct cp static struct freq_attr *acpi_cpufreq_attr[] = { &cpufreq_freq_attr_scaling_available_freqs, &freqdomain_cpus, - NULL, /* this is a placeholder for cpb, do not remove */ +#ifdef CONFIG_X86_ACPI_CPUFREQ_CPB + &cpb, +#endif NULL, }; @@ -957,17 +959,16 @@ static int __init acpi_cpufreq_init(void * only if configured. This is considered legacy code, which * will probably be removed at some point in the future. */ - if (check_amd_hwpstate_cpu(0)) { - struct freq_attr **iter; - - pr_debug("adding sysfs entry for cpb\n"); + if (!check_amd_hwpstate_cpu(0)) { + struct freq_attr **attr; - for (iter = acpi_cpufreq_attr; *iter != NULL; iter++) - ; + pr_debug("CPB unsupported, do not expose it\n"); - /* make sure there is a terminator behind it */ - if (iter[1] == NULL) - *iter = &cpb; + for (attr = acpi_cpufreq_attr; *attr; attr++) + if (*attr == &cpb) { + *attr = NULL; + break; + } } #endif acpi_cpufreq_boost_init(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/