4 files changed, 47 insertions, 8 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 47bbdf9c38d0..38f8d6553831 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -57,6 +57,7 @@ struct trace_iterator {
         /* The below is zeroed out in pipe_read */
         struct trace_seq        seq;
         struct trace_entry      *ent;
+        int                     leftover;
         int                     cpu;
         u64                     ts;
 
diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index 09077f6ed128..fad6857bc0f3 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -33,7 +33,7 @@ extern int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
         __attribute__ ((format (printf, 2, 0)));
 extern int
 trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary);
-extern void trace_print_seq(struct seq_file *m, struct trace_seq *s);
+extern int trace_print_seq(struct seq_file *m, struct trace_seq *s);
 extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
                                  size_t cnt);
 extern int trace_seq_puts(struct trace_seq *s, const char *str);
@@ -55,8 +55,9 @@ trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
         return 0;
 }
 
-static inline void trace_print_seq(struct seq_file *m, struct trace_seq *s)
+static inline int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
+        return 0;
 }
 static inline ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
                                  size_t cnt)
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)