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a="159787382" X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="159787382" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2020 06:51:39 -0700 IronPort-SDR: 7HR1W53DDbuBvI6KL+DvSwiZJc/6tu6ukrWAacRGhysPLoG/gLwERM2MIrx6/2oYw7GnBynZCm 8tdk06rxDjMQ== X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="308164089" Received: from mdioury-mobl.amr.corp.intel.com (HELO [10.213.184.164]) ([10.213.184.164]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2020 06:51:36 -0700 Subject: Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE To: Stephane Eranian , "Liang, Kan" Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , LKML , Mark Rutland , Alexander Shishkin , Jiri Olsa , Andi Kleen , kirill.shutemov@linux.intel.com, Michael Ellerman , benh@kernel.crashing.org, Paul Mackerras References: <20200921152653.3924-1-kan.liang@linux.intel.com> <20200921152653.3924-2-kan.liang@linux.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.