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Commit 2d542cf3 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

tracing/hw-branch-tracing: convert bts-tracer mutex to a spinlock 



Impact: fix CPU hotplug lockup

bts_hotcpu_handler() is called with irqs disabled, so using mutex_lock()
is a no-no.

All the BTS codepaths here are atomic (they do not schedule), so using
a spinlock is the right solution.

Cc: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 499aa86d

kernel/trace/trace_hw_branches.c

+28 −29
Original line number Diff line number Diff line
@@ -3,17 +3,15 @@ 
 *

 * Copyright (C) 2008-2009 Intel Corporation.

 * Markus Metzger <markus.t.metzger@gmail.com>, 2008-2009

 *

 */



#include <linux/module.h>

#include <linux/fs.h>

#include <linux/spinlock.h>

#include <linux/kallsyms.h>

#include <linux/debugfs.h>

#include <linux/ftrace.h>

#include <linux/kallsyms.h>

#include <linux/mutex.h>

#include <linux/module.h>

#include <linux/cpu.h>

#include <linux/smp.h>

#include <linux/fs.h>



#include <asm/ds.h>
@@ -23,16 +21,17 @@ 


#define SIZEOF_BTS (1 << 13)



/* The tracer mutex protects the below per-cpu tracer array.

   It needs to be held to:

   - start tracing on all cpus

   - stop tracing on all cpus

   - start tracing on a single hotplug cpu

   - stop tracing on a single hotplug cpu

   - read the trace from all cpus

   - read the trace from a single cpu

/*

 * The tracer lock protects the below per-cpu tracer array.

 * It needs to be held to:

 * - start tracing on all cpus

 * - stop tracing on all cpus

 * - start tracing on a single hotplug cpu

 * - stop tracing on a single hotplug cpu

 * - read the trace from all cpus

 * - read the trace from a single cpu

 */

static DEFINE_MUTEX(bts_tracer_mutex);

static DEFINE_SPINLOCK(bts_tracer_lock);

static DEFINE_PER_CPU(struct bts_tracer *, tracer);

static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer);
@@ -47,7 +46,7 @@ static struct trace_array *hw_branch_trace __read_mostly; 
 * Start tracing on the current cpu.

 * The argument is ignored.

 *

 * pre: bts_tracer_mutex must be locked.

 * pre: bts_tracer_lock must be locked.

 */

static void bts_trace_start_cpu(void *arg)

{
@@ -66,19 +65,19 @@ static void bts_trace_start_cpu(void *arg) 


static void bts_trace_start(struct trace_array *tr)

{

	mutex_lock(&bts_tracer_mutex);

	spin_lock(&bts_tracer_lock);



	on_each_cpu(bts_trace_start_cpu, NULL, 1);

	trace_hw_branches_enabled = 1;



	mutex_unlock(&bts_tracer_mutex);

	spin_unlock(&bts_tracer_lock);

}



/*

 * Stop tracing on the current cpu.

 * The argument is ignored.

 *

 * pre: bts_tracer_mutex must be locked.

 * pre: bts_tracer_lock must be locked.

 */

static void bts_trace_stop_cpu(void *arg)

{
@@ -90,12 +89,12 @@ static void bts_trace_stop_cpu(void *arg) 


static void bts_trace_stop(struct trace_array *tr)

{

	mutex_lock(&bts_tracer_mutex);

	spin_lock(&bts_tracer_lock);



	trace_hw_branches_enabled = 0;

	on_each_cpu(bts_trace_stop_cpu, NULL, 1);



	mutex_unlock(&bts_tracer_mutex);

	spin_unlock(&bts_tracer_lock);

}



static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
@@ -103,7 +102,7 @@ static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb, 
{

	unsigned int cpu = (unsigned long)hcpu;



	mutex_lock(&bts_tracer_mutex);

	spin_lock(&bts_tracer_lock);



	if (!trace_hw_branches_enabled)

		goto out;
@@ -119,7 +118,7 @@ static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb, 
	}



 out:

	mutex_unlock(&bts_tracer_mutex);

	spin_unlock(&bts_tracer_lock);

	return NOTIFY_DONE;

}
@@ -225,7 +224,7 @@ static void trace_bts_at(const struct bts_trace *trace, void *at) 
/*

 * Collect the trace on the current cpu and write it into the ftrace buffer.

 *

 * pre: bts_tracer_mutex must be locked

 * pre: bts_tracer_lock must be locked

 */

static void trace_bts_cpu(void *arg)

{
@@ -261,11 +260,11 @@ static void trace_bts_cpu(void *arg) 


static void trace_bts_prepare(struct trace_iterator *iter)

{

	mutex_lock(&bts_tracer_mutex);

	spin_lock(&bts_tracer_lock);



	on_each_cpu(trace_bts_cpu, iter->tr, 1);



	mutex_unlock(&bts_tracer_mutex);

	spin_unlock(&bts_tracer_lock);

}



static void trace_bts_close(struct trace_iterator *iter)
@@ -275,11 +274,11 @@ static void trace_bts_close(struct trace_iterator *iter) 


void trace_hw_branch_oops(void)

{

	mutex_lock(&bts_tracer_mutex);

	spin_lock(&bts_tracer_lock);



	trace_bts_cpu(hw_branch_trace);



	mutex_unlock(&bts_tracer_mutex);

	spin_unlock(&bts_tracer_lock);

}



struct tracer bts_tracer __read_mostly =