Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753381AbbGNCzT (ORCPT ); Mon, 13 Jul 2015 22:55:19 -0400 Received: from mga01.intel.com ([192.55.52.88]:47005 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752277AbbGNCzR (ORCPT ); Mon, 13 Jul 2015 22:55:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,468,1432623600"; d="scan'208";a="605628555" Message-ID: <55A47973.5080900@intel.com> Date: Tue, 14 Jul 2015 10:52:35 +0800 From: Pan Xinhui User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: "Rafael J. Wysocki" 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 References: <559F5D13.8050104@intel.com> <55A35BA4.8020800@intel.com> <1591472.jfYRX9HXXv@vostro.rjw.lan> <55A46F6B.6030006@intel.com> In-Reply-To: <55A46F6B.6030006@intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4615 Lines: 117 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[]. > > 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. >> >> -- 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/