Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161614AbaKNRWV (ORCPT ); Fri, 14 Nov 2014 12:22:21 -0500 Received: from smtprelay0022.hostedemail.com ([216.40.44.22]:55951 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1161017AbaKNRWO (ORCPT ); Fri, 14 Nov 2014 12:22:14 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2559:2562:2828:2901:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3874:4321:5007:6119:6261:6742:7903:8603:8660:10004:10400:10848:11026:11232:11473:11658:11914:12043:12296:12438:12517:12519:12740:13069:13148:13161:13229:13230:13311:13357:14096:14097:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: grain80_6a2f15298540e X-Filterd-Recvd-Size: 2735 Message-ID: <1415985728.5912.17.camel@perches.com> Subject: Re: [PATCH v2 1/2] kernel: printk: specify alignment for struct printk_log From: Joe Perches To: Andrey Ryabinin Cc: linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra , Sasha Levin , Randy Dunlap , Rasmus Villemoes , Jonathan Corbet , Michal Marek , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Yury Gribov , Dmitry Vyukov , Konstantin Khlebnikov , x86@kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org Date: Fri, 14 Nov 2014 09:22:08 -0800 In-Reply-To: <1415969446-26356-2-git-send-email-a.ryabinin@samsung.com> References: <1415969446-26356-1-git-send-email-a.ryabinin@samsung.com> <1415969446-26356-2-git-send-email-a.ryabinin@samsung.com> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2014-11-14 at 15:50 +0300, Andrey Ryabinin wrote: > On architectures that have support for efficient unaligned access > struct printk_log has 4-byte alignment. > Specify alignment attribute in type declaration. > > The whole point of this patch is to fix deadlock which happening > when UBSan detects unaligned access in printk() thus UBSan recursively > calls printk() with logbuf_lock held by top printk() call. [] > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c [] > @@ -223,7 +223,11 @@ struct printk_log { > u8 facility; /* syslog facility */ > u8 flags:5; /* internal record flags */ > u8 level:3; /* syslog level */ > -}; > +} > +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > +__packed __aligned(4) > +#endif Why is adding __packed useful or __aligned(4) useful? The struct is naturally aligned on u64 and should be the size of 2 u64s. struct printk_log { u64 ts_nsec; /* timestamp in nanoseconds */ u16 len; /* length of entire record */ u16 text_len; /* length of text buffer */ u16 dict_len; /* length of dictionary buffer */ u8 facility; /* syslog facility */ u8 flags:5; /* internal record flags */ u8 level:3; /* syslog level */ }; Is there any case when it's not sizeof(u64) * 2? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/