[PATCH] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

[Yang Jihong]

print_trace_line may overflow seq_file buffer. If the event is not
consumed, the while loop keeps peeking this event, causing a infinite loop.

Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---
 kernel/trace/trace.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 47a44b055a1d..2a8d5c68c29b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6788,6 +6788,19 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		if (ret == TRACE_TYPE_PARTIAL_LINE) {
 			/* don't print partial lines */
 			iter->seq.seq.len = save_len;
+
+			/*
+			 * If one trace_line of the tracer overflows seq_file
+			 * buffer, trace_seq_to_user returns -EBUSY because
+			 * nothing in the sequence (iter->seq.seq.len = \
+			 * iter->seq.seq.readpos = 0).
+			 * In this case, we need to consume, otherwise,
+			 * "while" will peek this event next time, resulting
+			 * in an infinite loop.
+			 */
+			if (trace_seq_has_overflowed(&iter->seq))
+				trace_consume(iter);
+
 			break;
 		}
 		if (ret != TRACE_TYPE_NO_CONSUME)
-- 
2.30.GIT