linux-kernel - Re: [PATCH v11 4/5] drivers/perf: add DesignWare PCIe PMU driver

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Message-ID: <2c092b76-6b76-4675-94c8-2e4b0031c966@linux.alibaba.com>
Date:   Wed, 6 Dec 2023 17:28:15 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Will Deacon <will@...nel.org>,
        Dan Carpenter <dan.carpenter@...aro.org>
Cc:     oe-kbuild@...ts.linux.dev, ilkka@...amperecomputing.com,
        kaishen@...ux.alibaba.com, helgaas@...nel.org,
        yangyicong@...wei.com, Jonathan.Cameron@...wei.com,
        baolin.wang@...ux.alibaba.com, robin.murphy@....com, lkp@...el.com,
        oe-kbuild-all@...ts.linux.dev, chengyou@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pci@...r.kernel.org, rdunlap@...radead.org,
        mark.rutland@....com, zhuo.song@...ux.alibaba.com,
        renyu.zj@...ux.alibaba.com
Subject: Re: [PATCH v11 4/5] drivers/perf: add DesignWare PCIe PMU driver



On 2023/12/5 22:21, Will Deacon wrote:
> On Sat, Nov 25, 2023 at 10:06:39AM +0300, Dan Carpenter wrote:
>> Hi Shuai,
>>
>> kernel test robot noticed the following build warnings:
>>
>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Shuai-Xue/docs-perf-Add-description-for-Synopsys-DesignWare-PCIe-PMU-driver/20231121-093713
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git next
>> patch link:    https://lore.kernel.org/r/20231121013400.18367-5-xueshuai%40linux.alibaba.com
>> patch subject: [PATCH v11 4/5] drivers/perf: add DesignWare PCIe PMU driver
>> config: x86_64-randconfig-r071-20231123 (https://download.01.org/0day-ci/archive/20231124/202311241906.0ymlLjyo-lkp@intel.com/config)
>> compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
>> reproduce: (https://download.01.org/0day-ci/archive/20231124/202311241906.0ymlLjyo-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@...el.com>
>> | Reported-by: Dan Carpenter <error27@...il.com>
>> | Closes: https://lore.kernel.org/r/202311241906.0ymlLjyo-lkp@intel.com/
>>
>> smatch warnings:
>> drivers/perf/dwc_pcie_pmu.c:352 dwc_pcie_pmu_event_update() error: uninitialized symbol 'now'.
>>
>> vim +/now +352 drivers/perf/dwc_pcie_pmu.c
>>
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  338  static void dwc_pcie_pmu_event_update(struct perf_event *event)
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  339  {
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  340  	struct hw_perf_event *hwc = &event->hw;
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  341  	enum dwc_pcie_event_type type = DWC_PCIE_EVENT_TYPE(event);
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  342  	u64 delta, prev, now;
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  343  
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  344  	do {
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  345  		prev = local64_read(&hwc->prev_count);
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  346  
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  347  		if (type == DWC_PCIE_LANE_EVENT)
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  348  			now = dwc_pcie_pmu_read_lane_event_counter(event);
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  349  		else if (type == DWC_PCIE_TIME_BASE_EVENT)
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  350  			now = dwc_pcie_pmu_read_time_based_counter(event);
>>
>> uninitialized on else path.
>>
>> 3481798a4ec51d1 Shuai Xue 2023-11-21  351  
>> 3481798a4ec51d1 Shuai Xue 2023-11-21 @352  	} while (local64_cmpxchg(&hwc->prev_count, prev, now) != prev);
> 
> Shuai, any chance you can address this please? I think the event validation
> logic means that the type is only ever one of the cases you handle, so
> you probably just want to either initialise 'now' to 0 or WARN and return
> early if the type is unknown.

Hi, Will, and Dan,

As the type is checked in dwc_pcie_pmu_event_init(), I will fix this warning by
initialising 'now' to 0.

Thank you.
Best Regards,
Shuai