tracing: Use flag buffer_disabled for irqsoff tracer
If the ring buffer is disabled and the irqsoff tracer records a trace it
will clear out its buffer and lose the data it had previously recorded.
Currently there's a callback when writing to the tracing_of file, but if
tracing is disabled via the function tracer trigger, it will not inform
the irqsoff tracer to stop recording.
By using the "mirror" flag (buffer_disabled) in the trace_array, that keeps
track of the status of the trace_array's buffer, it gives the irqsoff
tracer a fast way to know if it should record a new trace or not.
The flag may be a little behind the real state of the buffer, but it
should not affect the trace too much. It's more important for the irqsoff
tracer to be fast.
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c4c9296..0dc5071 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -226,9 +226,24 @@
return ts;
}
+/**
+ * tracing_is_enabled - Show if global_trace has been disabled
+ *
+ * Shows if the global trace has been enabled or not. It uses the
+ * mirror flag "buffer_disabled" to be used in fast paths such as for
+ * the irqsoff tracer. But it may be inaccurate due to races. If you
+ * need to know the accurate state, use tracing_is_on() which is a little
+ * slower, but accurate.
+ */
int tracing_is_enabled(void)
{
- return tracing_is_on();
+ /*
+ * For quick access (irqsoff uses this in fast path), just
+ * return the mirror variable of the state of the ring buffer.
+ * It's a little racy, but we don't really care.
+ */
+ smp_rmb();
+ return !global_trace.buffer_disabled;
}
/*
@@ -341,6 +356,23 @@
TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
+void tracer_tracing_on(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ ring_buffer_record_on(tr->trace_buffer.buffer);
+ /*
+ * This flag is looked at when buffers haven't been allocated
+ * yet, or by some tracers (like irqsoff), that just want to
+ * know if the ring buffer has been disabled, but it can handle
+ * races of where it gets disabled but we still do a record.
+ * As the check is in the fast path of the tracers, it is more
+ * important to be fast than accurate.
+ */
+ tr->buffer_disabled = 0;
+ /* Make the flag seen by readers */
+ smp_wmb();
+}
+
/**
* tracing_on - enable tracing buffers
*
@@ -349,15 +381,7 @@
*/
void tracing_on(void)
{
- if (global_trace.trace_buffer.buffer)
- ring_buffer_record_on(global_trace.trace_buffer.buffer);
- /*
- * This flag is only looked at when buffers haven't been
- * allocated yet. We don't really care about the race
- * between setting this flag and actually turning
- * on the buffer.
- */
- global_trace.buffer_disabled = 0;
+ tracer_tracing_on(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_on);
@@ -551,6 +575,23 @@
EXPORT_SYMBOL_GPL(tracing_snapshot_alloc);
#endif /* CONFIG_TRACER_SNAPSHOT */
+void tracer_tracing_off(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ ring_buffer_record_off(tr->trace_buffer.buffer);
+ /*
+ * This flag is looked at when buffers haven't been allocated
+ * yet, or by some tracers (like irqsoff), that just want to
+ * know if the ring buffer has been disabled, but it can handle
+ * races of where it gets disabled but we still do a record.
+ * As the check is in the fast path of the tracers, it is more
+ * important to be fast than accurate.
+ */
+ tr->buffer_disabled = 1;
+ /* Make the flag seen by readers */
+ smp_wmb();
+}
+
/**
* tracing_off - turn off tracing buffers
*
@@ -561,15 +602,7 @@
*/
void tracing_off(void)
{
- if (global_trace.trace_buffer.buffer)
- ring_buffer_record_off(global_trace.trace_buffer.buffer);
- /*
- * This flag is only looked at when buffers haven't been
- * allocated yet. We don't really care about the race
- * between setting this flag and actually turning
- * on the buffer.
- */
- global_trace.buffer_disabled = 1;
+ tracer_tracing_off(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_off);
@@ -580,13 +613,24 @@
}
/**
+ * tracer_tracing_is_on - show real state of ring buffer enabled
+ * @tr : the trace array to know if ring buffer is enabled
+ *
+ * Shows real state of the ring buffer if it is enabled or not.
+ */
+int tracer_tracing_is_on(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ return ring_buffer_record_is_on(tr->trace_buffer.buffer);
+ return !tr->buffer_disabled;
+}
+
+/**
* tracing_is_on - show state of ring buffers enabled
*/
int tracing_is_on(void)
{
- if (global_trace.trace_buffer.buffer)
- return ring_buffer_record_is_on(global_trace.trace_buffer.buffer);
- return !global_trace.buffer_disabled;
+ return tracer_tracing_is_on(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_is_on);
@@ -3958,7 +4002,7 @@
*
* iter->pos will be 0 if we haven't read anything.
*/
- if (!tracing_is_enabled() && iter->pos)
+ if (!tracing_is_on() && iter->pos)
break;
}
@@ -5631,15 +5675,10 @@
size_t cnt, loff_t *ppos)
{
struct trace_array *tr = filp->private_data;
- struct ring_buffer *buffer = tr->trace_buffer.buffer;
char buf[64];
int r;
- if (buffer)
- r = ring_buffer_record_is_on(buffer);
- else
- r = 0;
-
+ r = tracer_tracing_is_on(tr);
r = sprintf(buf, "%d\n", r);
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
@@ -5661,11 +5700,11 @@
if (buffer) {
mutex_lock(&trace_types_lock);
if (val) {
- ring_buffer_record_on(buffer);
+ tracer_tracing_on(tr);
if (tr->current_trace->start)
tr->current_trace->start(tr);
} else {
- ring_buffer_record_off(buffer);
+ tracer_tracing_off(tr);
if (tr->current_trace->stop)
tr->current_trace->stop(tr);
}
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index b19d065..2aefbee 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -373,7 +373,7 @@
struct trace_array_cpu *data;
unsigned long flags;
- if (likely(!tracer_enabled))
+ if (!tracer_enabled || !tracing_is_enabled())
return;
cpu = raw_smp_processor_id();
@@ -416,7 +416,7 @@
else
return;
- if (!tracer_enabled)
+ if (!tracer_enabled || !tracing_is_enabled())
return;
data = per_cpu_ptr(tr->trace_buffer.data, cpu);