From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f174.google.com (mail-lb0-f174.google.com [209.85.217.174]) by kanga.kvack.org (Postfix) with ESMTP id 2B5D19003C7 for ; Sun, 19 Jul 2015 19:17:53 -0400 (EDT) Received: by lbbzr7 with SMTP id zr7so86175313lbb.1 for ; Sun, 19 Jul 2015 16:17:52 -0700 (PDT) Received: from mail-lb0-x232.google.com (mail-lb0-x232.google.com. [2a00:1450:4010:c04::232]) by mx.google.com with ESMTPS id 6si16317343lai.40.2015.07.19.16.17.50 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 19 Jul 2015 16:17:51 -0700 (PDT) Received: by lbbzr7 with SMTP id zr7so86175054lbb.1 for ; Sun, 19 Jul 2015 16:17:50 -0700 (PDT) From: Rasmus Villemoes Subject: [RFC 3/3] slab.h: use check_mul_overflow in kmalloc_array Date: Mon, 20 Jul 2015 01:17:32 +0200 Message-Id: <1437347852-24921-3-git-send-email-linux@rasmusvillemoes.dk> In-Reply-To: <1437347852-24921-1-git-send-email-linux@rasmusvillemoes.dk> References: <1437347852-24921-1-git-send-email-linux@rasmusvillemoes.dk> Sender: owner-linux-mm@kvack.org List-ID: To: mingo@kernel.org, akpm@linux-foundation.org, Sasha Levin Cc: Rasmus Villemoes , linux-mm@kvack.org, linux-kernel@vger.kernel.org For recent enough gcc, check_mul_overflow maps to __builtin_mul_overflow, which on e.g. x86 allows gcc to do the multiplication and then check the overflow flag, instead of doing a separate comparison (which may even involve an expensive division, in the cases where size is not a compile-time constant). Unfortunately, it's not necessarily always a performance improvement: For example, when size is a compile-time constant power-of-2, gcc will now do the multiplication using the mul instruction instead of doing a comparison against an immediate and then a left shift for the multiplication. However, I think the compiler should be trusted to optimize the code - nothing prevents it from doing the overflow check the old way. Signed-off-by: Rasmus Villemoes --- include/linux/slab.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index a99f0e5243e1..82e49dee938d 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -14,6 +14,7 @@ #include #include #include +#include /* @@ -524,9 +525,11 @@ int memcg_update_all_caches(int num_memcgs); */ static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags) { - if (size != 0 && n > SIZE_MAX / size) + size_t prod; + + if (check_mul_overflow(n, size, &prod)) return NULL; - return __kmalloc(n * size, flags); + return __kmalloc(prod, flags); } /** -- 2.1.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org