[PATCH] ring_buffer: Ensure that buffer page data is aligned.

[Will Newton]

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.

Signed-off-by: Will Newton <will.newton@xxxxxxxxxx>
---
 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)
+
 /* 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 */
 };

 /*
-- 
1.7.3.4
From 356f15b861c41a65d4550358ab368fa01c36c77c Mon Sep 17 00:00:00 2001
From: Will Newton <will.newton@xxxxxxxxxx>
Date: Thu, 16 Jun 2011 13:38:59 +0100
Subject: [PATCH] ring_buffer: Ensure that buffer page data is aligned.

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.

Signed-off-by: Will Newton <will.newton@xxxxxxxxxx>
---
 kernel/trace/ring_buffer.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

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)
+
 /* 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 */
 };
 
 /*
-- 
1.7.3.4