From: Masami Hiramatsu (Google) <mhira...@kernel.org>
Reset the last-boot ring buffers when read() reads out all cpu
buffers through trace_pipe/trace_pipe_raw. This prevents ftrace to
unwind ring buffer read pointer next boot.
Note that this resets only when all per-cpu buffers are empty, and
read via read(2) syscall. For example, if you read only one of the
per-cpu trace_pipe, it does not reset it. Also, reading buffer by
splice(2) syscall, it does not reset because there will be the
data in reader page.
Suggested-by: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
kernel/trace/trace.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2c1764ed87b0..433671d3aa43 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6677,6 +6677,22 @@ static int tracing_wait_pipe(struct file *filp)
return 1;
}
+static bool update_last_data_if_empty(struct trace_array *tr)
+{
+ if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
+ return false;
+
+ if (!ring_buffer_empty(tr->array_buffer.buffer))
+ return false;
+
+ /*
+ * If the buffer contains the last boot data and all per-cpu
+ * buffers are empty, reset it from the kernel side.
+ */
+ update_last_data(tr);
+ return true;
+}
+
/*
* Consumer reader.
*/
@@ -6708,6 +6724,9 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
}
waitagain:
+ if (update_last_data_if_empty(iter->tr))
+ return 0;
+
sret = tracing_wait_pipe(filp);
if (sret <= 0)
return sret;
@@ -8286,6 +8305,9 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
if (ret < 0) {
if (trace_empty(iter) && !iter->closed) {
+ if (update_last_data_if_empty(iter->tr))
+ return 0;
+
if ((filp->f_flags & O_NONBLOCK))
return -EAGAIN;
