tracing/ftrace: fix pipe breaking

This patch fixes a bug which break the pipe when the seq is empty.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 2 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b38a4bb40548..6a1c76bb56ba 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2439,7 +2439,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
         if (sret != -EBUSY)
                 return sret;
-        sret = 0;
 
         trace_seq_reset(&iter->seq);
 
@@ -2450,6 +2449,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
                         goto out;
         }
 
+waitagain:
+        sret = 0;
         while (trace_empty(iter)) {
 
                 if ((filp->f_flags & O_NONBLOCK)) {
@@ -2556,8 +2557,13 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
         if (iter->seq.readpos >= iter->seq.len)
                 trace_seq_reset(&iter->seq);
+
+        /*
+         * If there was nothing to send to user, inspite of consuming trace
+         * entries, go back to wait for more entries.
+         */
         if (sret == -EBUSY)
-                sret = 0;
+                goto waitagain;
 
 out:
         mutex_unlock(&trace_types_lock);