Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757949Ab1FPNR0 (ORCPT ); Thu, 16 Jun 2011 09:17:26 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:44065 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752045Ab1FPNRV (ORCPT ); Thu, 16 Jun 2011 09:17:21 -0400 X-Authority-Analysis: v=1.1 cv=yMxAJ7W7nAoPh8ZdbvCArpG6pAdHwgpzIvOq8QbMesM= c=1 sm=0 a=0tApZq9ujVUA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=r_1tXGB3AAAA:8 a=1eaDYNr8cK8zg3hpklsA:9 a=iNyUJHFp_bhoJqoB2oUA:7 a=PUjeQqilurYA:10 a=EDSpbFuiShEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [PATCH] ring_buffer: Ensure that buffer page data is aligned. From: Steven Rostedt To: Will Newton Cc: Ingo Molnar , fweisbec@gmail.com, Linux Kernel list In-Reply-To: References: Content-Type: text/plain; charset="ISO-8859-15" Date: Thu, 16 Jun 2011 09:17:19 -0400 Message-ID: <1308230239.9218.137.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2433 Lines: 70 On Thu, 2011-06-16 at 14:03 +0100, Will Newton wrote: > Explicitly align the start of the buffer page data array to the > required arch alignment. This is required for architectures that > require 8 byte alignment but do not have a 8 byte local_t. What arch does that? A 32bit arch that forces 8 byte alignment? > > Signed-off-by: Will Newton > --- > kernel/trace/ring_buffer.c | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > I don't believe that any currently in-tree architecture is affected by > this, but it can be an issue on 32bit architectures that require an > 8 byte aligment but only have a 32bit local_t. I think it's potentially > cleaner to make the alignment explicit anyway. > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 0ef7b4b..36d5699 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -215,6 +215,8 @@ EXPORT_SYMBOL_GPL(tracing_is_on); > # define RB_ARCH_ALIGNMENT 8U > #endif > > +#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT) > + Note, the code above this is: #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array)) #define RB_ALIGNMENT 4U #define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) #define RB_EVNT_MIN_SIZE 8U /* two 32bit words */ #if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) # define RB_FORCE_8BYTE_ALIGNMENT 0 # define RB_ARCH_ALIGNMENT RB_ALIGNMENT #else # define RB_FORCE_8BYTE_ALIGNMENT 1 # define RB_ARCH_ALIGNMENT 8U #endif Which means that when CONFIG_64BIT is not set, RB_ARCH_ALIGNMENT is 4. This means that this patch is really a nop and doesn't do anything for your arch. -- Steve > /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */ > #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX > > @@ -363,7 +365,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data); > struct buffer_data_page { > u64 time_stamp; /* page time stamp */ > local_t commit; /* write committed index */ > - unsigned char data[]; /* data of buffer page */ > + unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */ > }; > > /* -- 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/