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SubjectRe: 3.5 regressions related to printk changes
On Sun, Jun 17, 2012 at 05:09:28PM +0200, Willy Tarreau wrote:
> Hi Kay,
> I was failing to get any 3.5-rc[123] kernel to boot on my dockstar (armv5).
> I finally found some time today to bisect it and found that the responsible
> commit was :
> From 7ff9554bb578ba02166071d2d487b7fc7d860d62 Mon Sep 17 00:00:00 2001
> From: Kay Sievers <>
> Date: Thu, 3 May 2012 02:29:13 +0200
> Subject: [PATCH] printk: convert byte-buffer to variable-length record buffer
> The symptom is that the kernel loads and hangs during early boot without
> displaying anything. My config had CONFIG_EARLY_PRINTK enabled so I tried
> without it again just in case it would be related, but it desperately did
> not change anything, the kernel still fails to boot.
> I have tried to revert printk changes on top of 3.5-rc3 and confirm that
> now the kernel properly boots. Here's the list of what I reverted for
> information :
> c313af145b9bc4fb8e8e0c83b8cfc10e1b894a50 printk() - isolate KERN_CONT users from ordinary complete lines
> 3ce9a7c0ac28561567fadedf1a99272e4970f740 printk() - restore prefix/timestamp printing for multi-newline str
> 1fce677971e29ceaa7c569741fa9c685a7b1052a printk: add stub for prepend_timestamp()
> f8450fca6ecdea38b5a882fdf6cd097e3ec8651c printk: correctly align __log_buf
> 649e6ee33f73ba1c4f2492c6de9aff2254b540cb printk() - restore timestamp printing at console output
> 5c5d5ca51abd728c8de3be43ffd6bb00f977bfcd printk() - do not merge continuation lines of different threads
> 7f3a781d6fd81e397c3928c9af33f1fc63232db6 printk - fix compilation for CONFIG_PRINTK=n
> 5fc3249068c1ed87c6fd485f42ced24132405629 kmsg: use do_div() to divide 64bit integer
> c4e00daaa96d3a0786f1f4fe6456281c60ef9a16 driver-core: extend dev_printk() to pass structured data
> e11fea92e13fb91c50bacca799a6131c81929986 kmsg: export printk records to the /dev/kmsg interface
> 7ff9554bb578ba02166071d2d487b7fc7d860d62 printk: convert byte-buffer to variable-length record buffer
> I understand that it will be hard to troubleshoot this with that little
> information :-/
> I'm not posting the config not to pollute the list, but have it available
> if needed. I haven't noticed anything seemingly related on the list, but
> if you want me to test a patch or to provide more information, feel free
> to suggest !
> I'm still checking if I can spot something.

Try the patch below, which is in my set of patches to go to Linus soon
and let me know if it works or not.


greg k-h

From 6ebb017de9d59a18c3ff9648270e8f6abaa93438 Mon Sep 17 00:00:00 2001
From: Andrew Lunn <>
Date: Tue, 5 Jun 2012 08:52:34 +0200
Subject: printk: Fix alignment of buf causing crash on ARM EABI

Commit 7ff9554bb578ba02166071d2d487b7fc7d860d62, printk: convert
byte-buffer to variable-length record buffer, causes systems using
EABI to crash very early in the boot cycle. The first entry in struct
log is a u64, which for EABI must be 8 byte aligned.

Make use of __alignof__() so the compiler to decide the alignment, but
allow it to be overridden using CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS,
for systems which can perform unaligned access and want to save
a few bytes of space.

Tested on Orion5x and Kirkwood.

Signed-off-by: Andrew Lunn <>
Tested-by: Stephen Warren <>
Acked-by: Stephen Warren <>
Acked-by: Kay Sievers <>
Signed-off-by: Greg Kroah-Hartman <>
kernel/printk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 32462d2..f205c25 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -227,10 +227,10 @@ static u32 clear_idx;
#define LOG_LINE_MAX 1024

/* record buffer */
#define LOG_ALIGN 4
-#define LOG_ALIGN 8
+#define LOG_ALIGN __alignof__(struct log)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);

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