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Subject: Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE
To:     Stephane Eranian <eranian@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        kirill.shutemov@linux.intel.com,
        Michael Ellerman <mpe@ellerman.id.au>,
        benh@kernel.crashing.org, Paul Mackerras <paulus@samba.org>
References: <20200921152653.3924-1-kan.liang@linux.intel.com>
 <20200921152653.3924-2-kan.liang@linux.intel.com>
 <CABPqkBRYzXH-76BZ3DdxYp7bdyPcr3_WxuxOsJw=1YPE9EwZaw@mail.gmail.com>
From:   "Liang, Kan" <kan.liang@linux.intel.com>
Message-ID: <4e974520-6d0f-68af-7eb8-fa52d95ba77b@linux.intel.com>
Date:   Wed, 30 Sep 2020 10:42:38 -0400
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On 9/30/2020 3:15 AM, Stephane Eranian wrote:
>> +static u64 perf_get_page_size(unsigned long addr)
>> +{
>> +       unsigned long flags;
>> +       u64 size;
>> +
>> +       if (!addr)
>> +               return 0;
>> +
>> +       /*
>> +        * Software page-table walkers must disable IRQs,
>> +        * which prevents any tear down of the page tables.
>> +        */
>> +       local_irq_save(flags);
>> +
>> +       size = __perf_get_page_size(current->active_mm, addr);
>> +
> When I tested on my kernel, it panicked because I suspect
> current->active_mm could be NULL. Adding a check for NULL avoided the
> problem. But I suspect this is not the correct solution.
> 

I guess the NULL active_mm should be a rare case. If so, I think it's 
not bad to add a check and return 0 page size.


Thanks,
Kan