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Subject[patch 1/2] dump_stack: serialize the output from dump_stack()
These patches fix up issues with interspersed output from multiple
simultaneous calls to warn or dump_stack on multi-cpu systems.
References: <20130508210102.898396979@asylum.americas.sgi.com>
Content-Disposition: inline; filename=dump-stack-serialize.patch

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

Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Reported-by: Russ Anderson <rja@sgi.com>
Reviewed-by: Robin Holt <holt@sgi.com>
Signed-off-by: Alex Thorlton <athorlton@sgi.com>
---
The original discussion regarding this patch can be found in this thread:
[PATCH] x86: Avoid intermixing cpu dump_stack output on multi-processor systems

lib/dump_stack.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

--- linux.orig/lib/dump_stack.c
+++ linux/lib/dump_stack.c
@@ -7,6 +7,8 @@
#include <linux/export.h>
#include <linux/sched.h>

+static atomic_t dump_lock = ATOMIC_INIT(-1);
+
/**
* dump_stack - dump the current task information and its stack trace
*
@@ -14,7 +16,30 @@
*/
void dump_stack(void)
{
+ int was_locked;
+ int old;
+ int cpu;
+
+ 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_print_info(KERN_DEFAULT);
show_stack(NULL, NULL);
+
+ if (!was_locked)
+ atomic_set(&dump_lock, -1);
+
+ preempt_enable();
}
EXPORT_SYMBOL(dump_stack);


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