From a1fdff0a8cfcd883146524c96d762d564deb3208 Mon Sep 17 00:00:00 2001
From: Alex Thorlton <athorlton@sgi.com>
Date: Fri, 28 Jun 2013 09:52:41 +1000
Subject: [PATCH] dump_stack: serialize the output from dump_stack()

tAdd adds functionality to serialize the output from dump_stack() to avoid
mangling of the output when dump_stack is called simultaneously from
multiple cpus.

Signed-off-by: Alex Thorlton <athorlton@sgi.com>
Reported-by: Russ Anderson <rja@sgi.com>
Reviewed-by: Robin Holt <holt@sgi.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 lib/dump_stack.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 53bad099ebd6..710884b6a989 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -6,15 +6,62 @@
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/sched.h>
+#include <asm/processor.h>
+#include <asm/atomic.h>
+
+#ifdef CONFIG_SMP
+#include <linux/smp.h>
+#endif
 
 /**
  * dump_stack - dump the current task information and its stack trace
  *
  * Architectures can override this implementation by implementing its own.
  */
+#ifdef CONFIG_SMP
+static atomic_t dump_lock = ATOMIC_INIT(-1);
+
 void dump_stack(void)
+{
+	int was_locked;
+	int old;
+	int cpu;
+
+        /*
+         * Permit this cpu to perform nested stack dumps while serialising
+         * against other CPUs
+         */
+	preempt_disable();
+
+retry:
+	cpu = smp_processor_id();
+	old = atomic_cmpxchg(&dump_lock, -1, cpu);
+	if (old == -1) {
+		was_locked = 0;
+	} else if (old == cpu) {
+		was_locked = 1;
+	} else {
+		cpu_relax();
+		goto retry;
+	}
+
+	__dump_stack();
+
+	if (!was_locked)
+		atomic_set(&dump_lock, -1);
+
+	preempt_enable();
+}
+#else
+void dump_stack(void)
+{
+	__dump_stack();
+}
+#endif
+EXPORT_SYMBOL(dump_stack);
+
+static void __dump_stack(void)
 {
 	dump_stack_print_info(KERN_DEFAULT);
 	show_stack(NULL, NULL);
 }
-EXPORT_SYMBOL(dump_stack);
-- 
2.39.5