Commit 5c9cf8af authored Jan 20, 2016 by Andrey Ryabinin Committed by Linus Torvalds Jan 20, 2016

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>

parent 41662f5c

kernel/printk/printk.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -233,7 +233,11 @@ 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
		;

		/*
		* The logbuf_lock protects kmsg buffer, indices, counters. This can be taken
		@@ -274,11 +278,7 @@ static u32 clear_idx;
		#define LOG_FACILITY(v) ((v) >> 3 & 0xff)

		/* 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_LEN (1 << CONFIG_LOG_BUF_SHIFT)
		static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
		static char *log_buf = __log_buf;

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