tracing: erase irqsoff trace with empty write

One convenient way to erase trace is "echo > trace". However, this is currently broken if the current tracer is irqsoff tracer. This is because irqsoff tracer use max_buffer as the default trace buffer.

Set the max_buffer as the one to be cleared when it's the trace buffer currently in use.

Signed-off-by Bo Yan <[email protected]>

---
 kernel/trace/trace.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

kernel/trace/trace.c +8 -2

index 5360b7aec57a..1f91bdd9365b 100644
@@ -4020,11 +4020,17 @@ static int tracing_open(struct inode *inode, struct file *file)
 	/* If this file was open for write, then erase contents */
 	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
 		int cpu = tracing_get_cpu(inode);
+		struct trace_buffer *tr_buf = &tr->trace_buffer;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+		if (tr->current_trace->print_max)
+			tr_buf = &tr->max_buffer;
+#endif
 
 		if (cpu == RING_BUFFER_ALL_CPUS)
-			tracing_reset_online_cpus(&tr->trace_buffer);
+			tracing_reset_online_cpus(tr_buf);
 		else
-			tracing_reset(&tr->trace_buffer, cpu);
+			tracing_reset(tr_buf, cpu);
 	}
 
 	if (file->f_mode & FMODE_READ) {

Quoted 7 lines · On Mon, 11 Sep 2017 11:16:35 -0700 Bo Yan <[email protected]> wrote:

One convenient way to erase trace is "echo > trace". However, this is currently broken if the current tracer is irqsoff tracer. This is because irqsoff tracer use max_buffer as the default trace buffer.

Set the max_buffer as the one to be cleared when it's the trace buffer currently in use.

Hi Bo,

I have no problems with the logic of the patch. But just one nit. The tr->trace_buffer has been called "trace_buf" elsewhere in the file. Can you resend with using the variable name "trace_buf" instead of "tr_buf" just to keep it consistent in the file. It's also been called 'buf' but trace_buf would probably be more appropriate.

Thanks!

-- Steve

Quoted 30 lines

Signed-off-by Bo Yan <[email protected]>

---
  kernel/trace/trace.c | 10 ++++++++--
  1 file changed, 8 insertions(+), 2 deletions(-)

kernel/trace/trace.c +8 -2

index 5360b7aec57a..1f91bdd9365b 100644
@@ -4020,11 +4020,17 @@ static int tracing_open(struct inode *inode, struct file *file)
  	/* If this file was open for write, then erase contents */
  	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
  		int cpu = tracing_get_cpu(inode);
+		struct trace_buffer *tr_buf = &tr->trace_buffer;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+		if (tr->current_trace->print_max)
+			tr_buf = &tr->max_buffer;
+#endif
 
  		if (cpu == RING_BUFFER_ALL_CPUS)
-			tracing_reset_online_cpus(&tr->trace_buffer);
+			tracing_reset_online_cpus(tr_buf);
  		else
-			tracing_reset(&tr->trace_buffer, cpu);
+			tracing_reset(tr_buf, cpu);
  	}
 
  	if (file->f_mode & FMODE_READ) {

Steven,

Thanks for review. I have posted the following update

https://lkml.org/lkml/2017/9/18/715