ring_buffer: tracing: Inherit the tracing setting to next ring buffer

Maintain the tracing on/off setting of the ring_buffer when switching to the trace buffer snapshot. Taking a snapshot is done by swapping the backup ring buffer (max_tr_buffer). But since the tracing on/off setting is defined by the ring buffer, when swapping it, the tracing on/off setting can also be changed. This causes a strange result like below: /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 0 > tracing_on /sys/kernel/debug/tracing # cat tracing_on 0 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 0 We don't touch tracing_on, but snapshot changes tracing_on setting each time. This is an anomaly, because user doesn't know that each "ring_buffer" stores its own tracing-enable state and the snapshot is done by swapping ring buffers. Link: http://lkml.kernel.org/r/153149929558.11274.11730609978254724394.stgit@devbox

Masami Hiramatsu committed 8 years ago

Commit 73c8d891 parent 1863c383 files · +23 −0Browse files

Showing the changes to kernel (2 of 3 files). Show all

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2 files

kernel/trace/ring_buffer.c +16 −0
kernel/trace/trace.c +6 −0

kernel/trace/ring_buffer.c+16−0

@@ -3226,6 +3226,22 @@ int ring_buffer_record_is_on(struct ring_buffer *buffer) · 3225 unmodified lines
3226	3226	return !atomic_read(&buffer->record_disabled);
3227	3227	}
3228	3228
	3229	+/**
	3230	+ * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
	3231	+ * @buffer: The ring buffer to see if write is set enabled
	3232	+ *
	3233	+ * Returns true if the ring buffer is set writable by ring_buffer_record_on().
	3234	+ * Note that this does NOT mean it is in a writable state.
	3235	+ *
	3236	+ * It may return true when the ring buffer has been disabled by
	3237	+ * ring_buffer_record_disable(), as that is a temporary disabling of
	3238	+ * the ring buffer.
	3239	+ */
	3240	+int ring_buffer_record_is_set_on(struct ring_buffer *buffer)
	3241	+{
	3242	+ return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
	3243	+}
	3244	+
3229	3245	/**
3230	3246	* ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3231	3247	* @buffer: The ring buffer to stop writes to.

kernel/trace/trace.c+6−0

@@ -1373,6 +1373,12 @@ update_max_tr(struct trace_array tr, struct task_struct tsk, int cpu) · 1372 unmodified lines
1373	1373
1374	1374	arch_spin_lock(&tr->max_lock);
1375	1375
	1376	+ /* Inherit the recordable setting from trace_buffer */
	1377	+ if (ring_buffer_record_is_set_on(tr->trace_buffer.buffer))
	1378	+ ring_buffer_record_on(tr->max_buffer.buffer);
	1379	+ else
	1380	+ ring_buffer_record_off(tr->max_buffer.buffer);
	1381	+
1376	1382	swap(tr->trace_buffer.buffer, tr->max_buffer.buffer);
1377	1383
1378	1384	__update_max_tr(tr, tsk, cpu);