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a="150247325" X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="150247325" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2020 07:48:51 -0700 IronPort-SDR: oZpWCVgBb3H5ehd2f3AWojh7zuEp+BHSx7QgPcs9pLQuRaILJbQjYM7Z/dZxgaSZ3m7r39lQ3Q THf+wwGsmR5A== X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="308182875" 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 07:48:50 -0700 Subject: Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE To: "Liang, Kan" , Stephane Eranian 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> <4e974520-6d0f-68af-7eb8-fa52d95ba77b@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: <4e974520-6d0f-68af-7eb8-fa52d95ba77b@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/30/20 7:42 AM, Liang, Kan wrote: >> 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. I think it would be best to understand why ->active_mm is NULL instead of just papering over the problem. If it is papered over, and this is common, you might end up effectively turning off your shiny new feature inadvertently.