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Subject[patch 31/74] tracing: Fix missing function_graph events when we splice_read from trace_pipe
2.6.30-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Lai Jiangshan <laijs@cn.fujitsu.com>

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>

---
kernel/trace/trace.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2993,7 +2993,8 @@ tracing_fill_pipe_page(size_t rem, struc
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_t
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);



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