Commit e2ace001 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Steven Rostedt
Browse files

tracing: Choose static tp_printk buffer by explicit nesting count 

Currently, the trace_printk code chooses which static buffer to use based
on what type of atomic context (NMI, IRQ, etc) it's in.  Simplify the
code and make it more robust: simply count the nesting depth and choose
a buffer based on the current nesting depth.

The new code will only drop an event if we nest more than 4 deep,
and the old code was guaranteed to malfunction if that happened.

Link: http://lkml.kernel.org/r/07ab03aecfba25fcce8f9a211b14c9c5e2865c58.1464289095.git.luto@kernel.org



Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 35abb67d

kernel/trace/trace.c

+24 −59
Original line number Diff line number Diff line
@@ -2339,83 +2339,41 @@ static void __trace_userstack(struct trace_array *tr, unsigned long flags) 


/* created for use with alloc_percpu */

struct trace_buffer_struct {

	char buffer[TRACE_BUF_SIZE];

	int nesting;

	char buffer[4][TRACE_BUF_SIZE];

};



static struct trace_buffer_struct *trace_percpu_buffer;

static struct trace_buffer_struct *trace_percpu_sirq_buffer;

static struct trace_buffer_struct *trace_percpu_irq_buffer;

static struct trace_buffer_struct *trace_percpu_nmi_buffer;



/*

 * The buffer used is dependent on the context. There is a per cpu

 * buffer for normal context, softirq contex, hard irq context and

 * for NMI context. Thise allows for lockless recording.

 *

 * Note, if the buffers failed to be allocated, then this returns NULL

 * Thise allows for lockless recording.  If we're nested too deeply, then

 * this returns NULL.

 */

static char *get_trace_buf(void)

{

	struct trace_buffer_struct *percpu_buffer;



	/*

	 * If we have allocated per cpu buffers, then we do not

	 * need to do any locking.

	 */

	if (in_nmi())

		percpu_buffer = trace_percpu_nmi_buffer;

	else if (in_irq())

		percpu_buffer = trace_percpu_irq_buffer;

	else if (in_softirq())

		percpu_buffer = trace_percpu_sirq_buffer;

	else

		percpu_buffer = trace_percpu_buffer;

	struct trace_buffer_struct *buffer = this_cpu_ptr(trace_percpu_buffer);



	if (!percpu_buffer)

	if (!buffer || buffer->nesting >= 4)

		return NULL;



	return this_cpu_ptr(&percpu_buffer->buffer[0]);

	return &buffer->buffer[buffer->nesting++][0];

}



static void put_trace_buf(void)

{

	this_cpu_dec(trace_percpu_buffer->nesting);

}



static int alloc_percpu_trace_buffer(void)

{

	struct trace_buffer_struct *buffers;

	struct trace_buffer_struct *sirq_buffers;

	struct trace_buffer_struct *irq_buffers;

	struct trace_buffer_struct *nmi_buffers;



	buffers = alloc_percpu(struct trace_buffer_struct);

	if (!buffers)

		goto err_warn;



	sirq_buffers = alloc_percpu(struct trace_buffer_struct);

	if (!sirq_buffers)

		goto err_sirq;



	irq_buffers = alloc_percpu(struct trace_buffer_struct);

	if (!irq_buffers)

		goto err_irq;



	nmi_buffers = alloc_percpu(struct trace_buffer_struct);

	if (!nmi_buffers)

		goto err_nmi;

	if (WARN(!buffers, "Could not allocate percpu trace_printk buffer"))

		return -ENOMEM;



	trace_percpu_buffer = buffers;

	trace_percpu_sirq_buffer = sirq_buffers;

	trace_percpu_irq_buffer = irq_buffers;

	trace_percpu_nmi_buffer = nmi_buffers;



	return 0;



 err_nmi:

	free_percpu(irq_buffers);

 err_irq:

	free_percpu(sirq_buffers);

 err_sirq:

	free_percpu(buffers);

 err_warn:

	WARN(1, "Could not allocate percpu trace_printk buffer");

	return -ENOMEM;

}



static int buffers_allocated;
@@ -2506,7 +2464,7 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args) 
	tbuffer = get_trace_buf();

	if (!tbuffer) {

		len = 0;

		goto out;

		goto out_nobuffer;

	}



	len = vbin_printf((u32 *)tbuffer, TRACE_BUF_SIZE/sizeof(int), fmt, args);
@@ -2532,6 +2490,9 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args) 
	}



out:

	put_trace_buf();



out_nobuffer:

	preempt_enable_notrace();

	unpause_graph_tracing();
@@ -2563,7 +2524,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, 
	tbuffer = get_trace_buf();

	if (!tbuffer) {

		len = 0;

		goto out;

		goto out_nobuffer;

	}



	len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args);
@@ -2582,7 +2543,11 @@ __trace_array_vprintk(struct ring_buffer *buffer, 
		__buffer_unlock_commit(buffer, event);

		ftrace_trace_stack(&global_trace, buffer, flags, 6, pc, NULL);

	}



out:

	put_trace_buf();



out_nobuffer:

	preempt_enable_notrace();

	unpause_graph_tracing();

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