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Subject[PATCH -tip 2/4] Tracing/ftrace: Fix pipe breaking
From: Pekka Paalanen <pq@iki.fi>

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

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/trace/trace.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 61f33da..ed10a68 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2610,7 +2610,6 @@ 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);

@@ -2621,6 +2620,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
goto out;
}

+waitagain:
+ sret = 0;
while (trace_empty(iter)) {

if ((filp->f_flags & O_NONBLOCK)) {
@@ -2754,8 +2755,13 @@ 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);

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