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Commit b32614c0 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Thomas Gleixner
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tracing/rb: Convert to hotplug state machine 



Install the callbacks via the state machine. The notifier in struct
ring_buffer is replaced by the multi instance interface.  Upon
__ring_buffer_alloc() invocation, cpuhp_state_add_instance() will invoke
the trace_rb_cpu_prepare() on each CPU.

This callback may now fail. This means __ring_buffer_alloc() will fail and
cleanup (like previously) and during a CPU up event this failure will not
allow the CPU to come up.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20161126231350.10321-7-bigeasy@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 14660b7e

include/linux/cpuhotplug.h

+1 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ enum cpuhp_state { 
	CPUHP_TOPOLOGY_PREPARE,

	CPUHP_NET_IUCV_PREPARE,

	CPUHP_ARM_BL_PREPARE,

	CPUHP_TRACE_RB_PREPARE,

	CPUHP_TIMERS_DEAD,

	CPUHP_NOTF_ERR_INJ_PREPARE,

	CPUHP_MIPS_SOC_PREPARE,

include/linux/ring_buffer.h

+6 −0
Original line number Diff line number Diff line
@@ -198,4 +198,10 @@ enum ring_buffer_flags { 
	RB_FL_OVERWRITE		= 1 << 0,

};



#ifdef CONFIG_RING_BUFFER

int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node);

#else

#define trace_rb_cpu_prepare	NULL

#endif



#endif /* _LINUX_RING_BUFFER_H */

kernel/trace/ring_buffer.c

+45 −90
Original line number Diff line number Diff line
@@ -479,9 +479,7 @@ struct ring_buffer { 


	struct ring_buffer_per_cpu	**buffers;



#ifdef CONFIG_HOTPLUG_CPU

	struct notifier_block		cpu_notify;

#endif

	struct hlist_node		node;

	u64				(*clock)(void);



	struct rb_irq_work		irq_work;
@@ -1274,11 +1272,6 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer) 
	kfree(cpu_buffer);

}



#ifdef CONFIG_HOTPLUG_CPU

static int rb_cpu_notify(struct notifier_block *self,

			 unsigned long action, void *hcpu);

#endif



/**

 * __ring_buffer_alloc - allocate a new ring_buffer

 * @size: the size in bytes per cpu that is needed.
@@ -1296,6 +1289,7 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 
	long nr_pages;

	int bsize;

	int cpu;

	int ret;



	/* keep it in its own cache line */

	buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
@@ -1318,17 +1312,6 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 
	if (nr_pages < 2)

		nr_pages = 2;



	/*

	 * In case of non-hotplug cpu, if the ring-buffer is allocated

	 * in early initcall, it will not be notified of secondary cpus.

	 * In that off case, we need to allocate for all possible cpus.

	 */

#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_begin();

	cpumask_copy(buffer->cpumask, cpu_online_mask);

#else

	cpumask_copy(buffer->cpumask, cpu_possible_mask);

#endif

	buffer->cpus = nr_cpu_ids;



	bsize = sizeof(void *) * nr_cpu_ids;
@@ -1337,19 +1320,15 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 
	if (!buffer->buffers)

		goto fail_free_cpumask;



	for_each_buffer_cpu(buffer, cpu) {

		buffer->buffers[cpu] =

			rb_allocate_cpu_buffer(buffer, nr_pages, cpu);

	cpu = raw_smp_processor_id();

	cpumask_set_cpu(cpu, buffer->cpumask);

	buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);

	if (!buffer->buffers[cpu])

		goto fail_free_buffers;

	}



#ifdef CONFIG_HOTPLUG_CPU

	buffer->cpu_notify.notifier_call = rb_cpu_notify;

	buffer->cpu_notify.priority = 0;

	__register_cpu_notifier(&buffer->cpu_notify);

	cpu_notifier_register_done();

#endif

	ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);

	if (ret < 0)

		goto fail_free_buffers;



	mutex_init(&buffer->mutex);
@@ -1364,9 +1343,6 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 


 fail_free_cpumask:

	free_cpumask_var(buffer->cpumask);

#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_done();

#endif



 fail_free_buffer:

	kfree(buffer);
@@ -1383,18 +1359,11 @@ ring_buffer_free(struct ring_buffer *buffer) 
{

	int cpu;



#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_begin();

	__unregister_cpu_notifier(&buffer->cpu_notify);

#endif

	cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);



	for_each_buffer_cpu(buffer, cpu)

		rb_free_cpu_buffer(buffer->buffers[cpu]);



#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_done();

#endif



	kfree(buffer->buffers);

	free_cpumask_var(buffer->cpumask);
@@ -4633,22 +4602,21 @@ int ring_buffer_read_page(struct ring_buffer *buffer, 
}

EXPORT_SYMBOL_GPL(ring_buffer_read_page);



#ifdef CONFIG_HOTPLUG_CPU

static int rb_cpu_notify(struct notifier_block *self,

			 unsigned long action, void *hcpu)

/*

 * We only allocate new buffers, never free them if the CPU goes down.

 * If we were to free the buffer, then the user would lose any trace that was in

 * the buffer.

 */

int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)

{

	struct ring_buffer *buffer =

		container_of(self, struct ring_buffer, cpu_notify);

	long cpu = (long)hcpu;

	struct ring_buffer *buffer;

	long nr_pages_same;

	int cpu_i;

	unsigned long nr_pages;



	switch (action) {

	case CPU_UP_PREPARE:

	case CPU_UP_PREPARE_FROZEN:

	buffer = container_of(node, struct ring_buffer, node);

	if (cpumask_test_cpu(cpu, buffer->cpumask))

			return NOTIFY_OK;

		return 0;



	nr_pages = 0;

	nr_pages_same = 1;
@@ -4668,27 +4636,14 @@ static int rb_cpu_notify(struct notifier_block *self, 
	buffer->buffers[cpu] =

		rb_allocate_cpu_buffer(buffer, nr_pages, cpu);

	if (!buffer->buffers[cpu]) {

			WARN(1, "failed to allocate ring buffer on CPU %ld\n",

		WARN(1, "failed to allocate ring buffer on CPU %u\n",

		     cpu);

			return NOTIFY_OK;

		return -ENOMEM;

	}

	smp_wmb();

	cpumask_set_cpu(cpu, buffer->cpumask);

		break;

	case CPU_DOWN_PREPARE:

	case CPU_DOWN_PREPARE_FROZEN:

		/*

		 * Do nothing.

		 *  If we were to free the buffer, then the user would

		 *  lose any trace that was in the buffer.

		 */

		break;

	default:

		break;

	}

	return NOTIFY_OK;

	return 0;

}

#endif



#ifdef CONFIG_RING_BUFFER_STARTUP_TEST

/*

kernel/trace/trace.c

+14 −1
Original line number Diff line number Diff line
@@ -7659,10 +7659,21 @@ __init static int tracer_alloc_buffers(void) 


	raw_spin_lock_init(&global_trace.start_lock);



	/*

	 * The prepare callbacks allocates some memory for the ring buffer. We

	 * don't free the buffer if the if the CPU goes down. If we were to free

	 * the buffer, then the user would lose any trace that was in the

	 * buffer. The memory will be removed once the "instance" is removed.

	 */

	ret = cpuhp_setup_state_multi(CPUHP_TRACE_RB_PREPARE,

				      "trace/RB:preapre", trace_rb_cpu_prepare,

				      NULL);

	if (ret < 0)

		goto out_free_cpumask;

	/* Used for event triggers */

	temp_buffer = ring_buffer_alloc(PAGE_SIZE, RB_FL_OVERWRITE);

	if (!temp_buffer)

		goto out_free_cpumask;

		goto out_rm_hp_state;



	if (trace_create_savedcmd() < 0)

		goto out_free_temp_buffer;
@@ -7723,6 +7734,8 @@ __init static int tracer_alloc_buffers(void) 
	free_saved_cmdlines_buffer(savedcmd);

out_free_temp_buffer:

	ring_buffer_free(temp_buffer);

out_rm_hp_state:

	cpuhp_remove_multi_state(CPUHP_TRACE_RB_PREPARE);

out_free_cpumask:

	free_cpumask_var(global_trace.tracing_cpumask);

out_free_buffer_mask: