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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b38a4bb40548811ad4d4aa7b0b0c5cc5d229cc96..6a1c76bb56ba8f3998936ce476f111e8f21f75cc 100644 (file)
--- 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);