From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Date: Wed, 20 Jan 2016 23:00:48 +0000 (-0800)
Subject: kernel: printk: specify alignment for struct printk_log
X-Git-Tag: submit/tizen/20160810.050017~159
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a0334ef6460ac92276f0fa9c4adee5d6320ffb41;p=platform%2Fkernel%2Flinux-exynos.git

kernel: printk: specify alignment for struct printk_log

On architectures that have support for efficient unaligned access struct
printk_log has 4-byte alignment.  Specify alignment attribute in type
declaration.

The whole point of this patch is to fix deadlock which happening when
UBSAN detects unaligned access in printk() thus UBSAN recursively calls
printk() with logbuf_lock held by top printk() call.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Yury Gribov <y.gribov@samsung.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kostya Serebryany <kcc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[Backport from mainline for UBSAN]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>

Change-Id: I93d23dec2c1539faf21eb7242ccc328999950c01
---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2a38f63adf43..4a6dce9a3467 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -228,7 +228,11 @@ struct printk_log {
 	u8 facility;		/* syslog facility */
 	u8 flags:5;		/* internal record flags */
 	u8 level:3;		/* syslog level */
-};
+}
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+__packed __aligned(4)
+#endif
+;
 
 struct log_buffer {
 #ifdef CONFIG_PRINTK
@@ -276,11 +280,7 @@ static enum log_flags console_prev;
 #define KMSG_NUM_MAX    255
 
 /* record buffer */
-#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
-#define LOG_ALIGN 4
-#else
 #define LOG_ALIGN __alignof__(struct printk_log)
-#endif
 #define __LOG_BUF_K_LEN (1 << CONFIG_LOG_BUF_SHIFT)
 static char __log_buf_k[__LOG_BUF_K_LEN] __aligned(LOG_ALIGN);