linux-kernel - Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Message-ID: <96c37bf7-7dc9-5895-be76-cc52a032709f@intel.com>
Date:   Wed, 30 Sep 2020 06:51:35 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Stephane Eranian <eranian@...gle.com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
        kirill.shutemov@...ux.intel.com,
        Michael Ellerman <mpe@...erman.id.au>,
        benh@...nel.crashing.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

On 9/30/20 12:15 AM, Stephane Eranian wrote:
>> +       /*
>> +        * 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.

Did you happen to capture the oops?  I can _imagine_ scenarios where
current->active_mm could be NULL, I just can't find any obvious ones in
the code.