2 files changed, 43 insertions, 6 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dc937e1baa91..484114d70743 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1516,6 +1516,8 @@ static void *s_next(struct seq_file *m, void *v, loff_t *pos)
 	int i = (int)*pos;
 	void *ent;
 
+	WARN_ON_ONCE(iter->leftover);
+
 	(*pos)++;
 
 	/* can't go backwards */
@@ -1614,8 +1616,16 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 			;
 
 	} else {
-		l = *pos - 1;
-		p = s_next(m, p, &l);
+		/*
+		 * If we overflowed the seq_file before, then we want
+		 * to just reuse the trace_seq buffer again.
+		 */
+		if (iter->leftover)
+			p = iter;
+		else {
+			l = *pos - 1;
+			p = s_next(m, p, &l);
+		}
 	}
 
 	trace_event_read_lock();
@@ -1923,6 +1933,7 @@ static enum print_line_t print_trace_line(struct trace_iterator *iter)
 static int s_show(struct seq_file *m, void *v)
 {
 	struct trace_iterator *iter = v;
+	int ret;
 
 	if (iter->ent == NULL) {
 		if (iter->tr) {
@@ -1942,9 +1953,27 @@ static int s_show(struct seq_file *m, void *v)
 			if (!(trace_flags & TRACE_ITER_VERBOSE))
 				print_func_help_header(m);
 		}
+	} else if (iter->leftover) {
+		/*
+		 * If we filled the seq_file buffer earlier, we
+		 * want to just show it now.
+		 */
+		ret = trace_print_seq(m, &iter->seq);
+
+		/* ret should this time be zero, but you never know */
+		iter->leftover = ret;
+
 	} else {
 		print_trace_line(iter);
-		trace_print_seq(m, &iter->seq);
+		ret = trace_print_seq(m, &iter->seq);
+		/*
+		 * If we overflow the seq_file buffer, then it will
+		 * ask us for this data again at start up.
+		 * Use that instead.
+		 *  ret is 0 if seq_file write succeeded.
+		 *        -1 otherwise.
+		 */
+		iter->leftover = ret;
 	}
 
 	return 0;
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index b6c12c6a1bcd..e5cf90fef34e 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -23,13 +23,21 @@ static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
 
 static int next_event_type = __TRACE_LAST_TYPE + 1;
 
-void trace_print_seq(struct seq_file *m, struct trace_seq *s)
+int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
 	int len = s->len >= PAGE_SIZE ? PAGE_SIZE - 1 : s->len;
+	int ret;
+
+	ret = seq_write(m, s->buffer, len);
 
-	seq_write(m, s->buffer, len);
+	/*
+	 * Only reset this buffer if we successfully wrote to the
+	 * seq_file buffer.
+	 */
+	if (!ret)
+		trace_seq_init(s);
 
-	trace_seq_init(s);
+	return ret;
 }
 
 enum print_line_t trace_print_bprintk_msg_only(struct trace_iterator *iter)