From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756244AbaFRUpu (ORCPT ); Wed, 18 Jun 2014 16:45:50 -0400 Received: from mail-pb0-f44.google.com ([209.85.160.44]:38985 "EHLO mail-pb0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755096AbaFRUps (ORCPT ); Wed, 18 Jun 2014 16:45:48 -0400 From: "Luis R. Rodriguez" To: gregkh@linuxfoundation.org, akpm@linux-foundation.org, hpa@linux.intel.com Cc: linux-kernel@vger.kernel.org, "Luis R. Rodriguez" , Andrew Lunn , Stephen Warren , Michal Hocko , Petr Mladek , Joe Perches , Arun KS , Kees Cook , Davidlohr Bueso , Chris Metcalf Subject: [PATCH v8 1/4] printk: make dynamic kernel ring buffer alignment explicit Date: Wed, 18 Jun 2014 13:45:34 -0700 Message-Id: <1403124337-14886-1-git-send-email-mcgrof@do-not-panic.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Luis R. Rodriguez" We have to consider alignment for the ring buffer both for the default static size, and then also for when an dynamic allocation is made when the log_buf_len=n kernel parameter is passed to set the size specifically to a size larger than the default size set by the architecture through CONFIG_LOG_BUF_SHIFT. The default static kernel ring buffer can be aligned properly if architectures set CONFIG_LOG_BUF_SHIFT properly, we provide ranges for the size though so even if CONFIG_LOG_BUF_SHIFT has a sensible aligned value it can be reduced to a non aligned value. Commit 6ebb017de9 by Andrew ensures the static buffer is always aligned and the decision of alignment is done by the compiler by using __alignof__(struct log). When log_buf_len=n is used we allocate the ring buffer dynamically. Dynamic allocation varies, for the early allocation called before setup_arch() memblock_virt_alloc() requests a page aligment and for the default kernel allocation memblock_virt_alloc_nopanic() requests no special alignment, which in turn ends up aligning the allocation to SMP_CACHE_BYTES, which is L1 cache aligned. Since we already have the required alignment for the kernel ring buffer though we can do better and request explicit alignment for LOG_ALIGN. This does that to be safe and make dynamic allocation alignment explicit. Cc: Andrew Lunn Cc: Stephen Warren Cc: Greg Kroah-Hartman Cc: Michal Hocko Cc: Petr Mladek Cc: Andrew Morton Cc: Joe Perches Cc: Arun KS Cc: Kees Cook Cc: Davidlohr Bueso Cc: Chris Metcalf Cc: linux-kernel@vger.kernel.org Acked-by: Petr Mladek Tested-by: Petr Mladek Signed-off-by: Luis R. Rodriguez --- kernel/printk/printk.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ea2d5f6..78ceccf 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -853,9 +853,10 @@ void __init setup_log_buf(int early) if (early) { new_log_buf = - memblock_virt_alloc(new_log_buf_len, PAGE_SIZE); + memblock_virt_alloc(new_log_buf_len, LOG_ALIGN); } else { - new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len, 0); + new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len, + LOG_ALIGN); } if (unlikely(!new_log_buf)) { -- 1.9.3