tracing: Fix missing function_graph events when we splice_read from trace_pipe

commit 74e7ff8c50b6b022e6ffaa736b16a4dc161d3eaf upstream.

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>
LKML-Reference: <4A6EEC52.90704@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index cda81ec58d9fe1e723388826de8966b274b71d0a..3928aeecdf90311bd773c3040648aa330cd26142 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2993,7 +2993,8 @@ 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;
@@ -4122,8 +4123,11 @@ 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);