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

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Message-ID: <20231205142128.GA18450@willie-the-truck>
Date:   Tue, 5 Dec 2023 14:21:28 +0000
From:   Will Deacon <will@...nel.org>
To:     Dan Carpenter <dan.carpenter@...aro.org>
Cc:     oe-kbuild@...ts.linux.dev, Shuai Xue <xueshuai@...ux.alibaba.com>,
        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 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.

Will