tracing: Fix missing function_graph events when we splice_read from trace_pipe

About a half events are missing when we splice_read
from trace_pipe. They are unexpectedly consumed because we ignore
the TRACE_TYPE_NO_CONSUME return value used by the function graph
tracer when it needs to consume the events by itself to walk on
the ring buffer.

The same problem appears with ftrace_dump()

Example of an output before this patch:

1)               |      ktime_get_real() {
1)   2.846 us    |          read_hpet();
1)   4.558 us    |        }
1)   6.195 us    |      }

After this patch:

0)               |      ktime_get_real() {
0)               |        getnstimeofday() {
0)   1.960 us    |          read_hpet();
0)   3.597 us    |        }
0)   5.196 us    |      }

The fix also applies on 2.6.30

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: stable@kernel.org
LKML-Reference: <4A6EEC52.90704@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8bc8d8afea6a..da984ad065ab 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3085,7 +3085,8 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
                         break;
                 }
 
-                trace_consume(iter);
+                if (ret != TRACE_TYPE_NO_CONSUME)
+                        trace_consume(iter);
                 rem -= count;
                 if (!find_next_entry_inc(iter)) {
                         rem = 0;
@@ -4233,8 +4234,11 @@ static void __ftrace_dump(bool disable_tracing)
                 iter.pos = -1;
 
                 if (find_next_entry_inc(&iter) != NULL) {
-                        print_trace_line(&iter);
-                        trace_consume(&iter);
+                        int ret;
+
+                        ret = print_trace_line(&iter);
+                        if (ret != TRACE_TYPE_NO_CONSUME)
+                                trace_consume(&iter);
                 }
 
                 trace_printk_seq(&iter.seq);