linux-kernel - [PATCH 6/7] dump_stack: Serialise dump_stack with die_spin_lock

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Date:	Tue, 24 Feb 2015 14:30:33 +1100
From:	Anton Blanchard <anton@...ba.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	sam.bobroff@....ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
	Russell King <linux@....linux.org.uk>, peterz@...radead.org,
	Don Zickus <dzickus@...hat.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: [PATCH 6/7] dump_stack: Serialise dump_stack with die_spin_lock_{irqsave,irqrestore}

Remove another version of a recursive lock in dump_stack.

Signed-off-by: Anton Blanchard <anton@...ba.org>
---
 lib/dump_stack.c | 40 ++++------------------------------------
 1 file changed, 4 insertions(+), 36 deletions(-)

diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 6745c62..f64ee3c 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -7,7 +7,7 @@
 #include <linux/export.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
-#include <linux/atomic.h>
+#include <linux/die_lock.h>
 
 static void __dump_stack(void)
 {
@@ -20,44 +20,12 @@ static void __dump_stack(void)
  *
  * Architectures can override this implementation by implementing its own.
  */
-#ifdef CONFIG_SMP
-static atomic_t dump_lock = ATOMIC_INIT(-1);
-
 asmlinkage __visible 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();
+	unsigned long flags;
 
-	if (!was_locked)
-		atomic_set(&dump_lock, -1);
-
-	preempt_enable();
-}
-#else
-asmlinkage __visible void dump_stack(void)
-{
+	die_spin_lock_irqsave(flags);
 	__dump_stack();
+	die_spin_unlock_irqrestore(flags);
 }
-#endif
 EXPORT_SYMBOL(dump_stack);
-- 
2.1.0

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