From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756744AbdCUJY4 (ORCPT ); Tue, 21 Mar 2017 05:24:56 -0400 Received: from mail-he1eur01on0135.outbound.protection.outlook.com ([104.47.0.135]:44404 "EHLO EUR01-HE1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756440AbdCUJYz (ORCPT ); Tue, 21 Mar 2017 05:24:55 -0400 Authentication-Results: vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=virtuozzo.com; Subject: Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations To: Mark Rutland , Dmitry Vyukov References: <6bb1c71b87b300d04977c34f0cd8586363bc6170.1489519233.git.dvyukov@google.com> <20170320171718.GL31213@leverpostej> CC: , , , , , , , From: Andrey Ryabinin Message-ID: <956a8e10-e03f-a21c-99d9-8a75c2616e0a@virtuozzo.com> Date: Tue, 21 Mar 2017 12:25:06 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; 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>> + /* >> + * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN >> + * instrumentation. Double instrumentation is unnecessary. >> + */ >> + return READ_ONCE_NOCHECK((v)->counter); >> } > > Just to check, we do this to avoid duplicate reports, right? > > If so, double instrumentation isn't solely "unnecessary"; it has a > functional difference, and we should explicitly describe that in the > comment. > > ... or are duplicate reports supressed somehow? > They are not suppressed yet. But I think we should just switch kasan to single shot mode, i.e. report only the first error. Single bug quite often has multiple invalid memory accesses causing storm in dmesg. Also write OOB might corrupt metadata so the next report will print bogus alloc/free stacktraces. In most cases we need to look only at the first report, so reporting anything after the first is just counterproductive.