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Subject: Re: [PATCH v3] perf/core: Fix reentry problem in
 perf_output_read_group
To:     Peter Zijlstra <peterz@infradead.org>
CC:     <rostedt@goodmis.org>, <mingo@redhat.com>, <acme@kernel.org>,
        <mark.rutland@arm.com>, <alexander.shishkin@linux.intel.com>,
        <jolsa@kernel.org>, <namhyung@kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-perf-users@vger.kernel.org>
References: <20220816091103.257702-1-yangjihong1@huawei.com>
 <YvumDL1qz1NjpfEC@worktop.programming.kicks-ass.net>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <eef9a64a-6f3a-01cb-ec06-1b6da0102217@huawei.com>
Date:   Wed, 17 Aug 2022 11:18:26 +0800
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Hello,

On 2022/8/16 22:13, Peter Zijlstra wrote:
> On Tue, Aug 16, 2022 at 05:11:03PM +0800, Yang Jihong wrote:
>> perf_output_read_group may respond to IPI request of other cores and invoke
>> __perf_install_in_context function. As a result, hwc configuration is modified.
>> As a result, the hwc configuration is modified, causing inconsistency and
>> unexpected consequences.
> 
>>   read_pmevcntrn+0x1e4/0x1ec arch/arm64/kernel/perf_event.c:423
>>   armv8pmu_read_evcntr arch/arm64/kernel/perf_event.c:467 [inline]
>>   armv8pmu_read_hw_counter arch/arm64/kernel/perf_event.c:475 [inline]
>>   armv8pmu_read_counter+0x10c/0x1f0 arch/arm64/kernel/perf_event.c:528
>>   armpmu_event_update+0x9c/0x1bc drivers/perf/arm_pmu.c:247
>>   armpmu_read+0x24/0x30 drivers/perf/arm_pmu.c:264
>>   perf_output_read_group+0x4cc/0x71c kernel/events/core.c:6806
>>   perf_output_read+0x78/0x1c4 kernel/events/core.c:6845
>>   perf_output_sample+0xafc/0x1000 kernel/events/core.c:6892
>>   __perf_event_output kernel/events/core.c:7273 [inline]
>>   perf_event_output_forward+0xd8/0x130 kernel/events/core.c:7287
>>   __perf_event_overflow+0xbc/0x20c kernel/events/core.c:8943
>>   perf_swevent_overflow kernel/events/core.c:9019 [inline]
>>   perf_swevent_event+0x274/0x2c0 kernel/events/core.c:9047
>>   do_perf_sw_event kernel/events/core.c:9160 [inline]
>>   ___perf_sw_event+0x150/0x1b4 kernel/events/core.c:9191
>>   __perf_sw_event+0x58/0x7c kernel/events/core.c:9203
>>   perf_sw_event include/linux/perf_event.h:1177 [inline]
> 
>> Interrupts is not disabled when perf_output_read_group reads PMU counter.
> 
> s/is/are/ due to 'interrupts' being plural
Ok, will fix in next version.
> 
> Anyway, yes, I suppose this is indeed so. That code expects to run with
> IRQs disabled but in the case of software events that isn't so.
> 
Do we need to determine whether it is a software event?
It feels like it's simply disable IRQs interrupts, with little impact.
>> In this case, IPI request may be received from other cores.
>> As a result, PMU configuration is modified and an error occurs when
>> reading PMU counter:

<SNIP>


Thanks,
Yang