4.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
commit d6726c8145290bef950ae2538ea6ae1d96a1944b upstream.
He Kuang noticed that the trace event samples for arrays was broken:
"The output result of trace_foo_bar event in traceevent samples is
wrong. This problem can be reproduced as following:
(Build kernel with SAMPLE_TRACE_EVENTS=m)
$ insmod trace-events-sample.ko
$ echo 1 > /sys/kernel/debug/tracing/events/sample-trace/foo_bar/enable
$ cat /sys/kernel/debug/tracing/trace
event-sample-980 [000] .... 43.649559: foo_bar: foo hello 21 0x15
BIT1|BIT3|0x10 {0x1,0x6f6f6e53,0xff007970,0xffffffff} Snoopy
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The array length is not right, should be {0x1}.
(ffffffff,ffffffff)
event-sample-980 [000] .... 44.653827: foo_bar: foo hello 22 0x16
BIT2|BIT3|0x10
{0x1,0x2,0x646e6147,0x666c61,0xffffffff,0xffffffff,0x750aeffe,0x7}
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The array length is not right, should be {0x1,0x2}.
Gandalf (ffffffff,ffffffff)"
This was caused by an update to have __print_array()'s second parameter
be the count of items in the array and not the size of the array.
As there is already users of __print_array(), it can not change. But
the sample code can and we can also improve on the documentation about
__print_array() and __get_dynamic_array_len().
Link: http://lkml.kernel.org/r/1436839171-31527-2-git-send-email-hekuang@xxxxxxxxxx
Fixes: ac01ce1410fc2 ("tracing: Make ftrace_print_array_seq compute buf_len")
Reported-by: He Kuang <hekuang@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
samples/trace_events/trace-events-sample.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/samples/trace_events/trace-events-sample.h
+++ b/samples/trace_events/trace-events-sample.h
@@ -168,7 +168,10 @@
*
* For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo)
* Use __get_dynamic_array_len(foo) to get the length of the array
- * saved.
+ * saved. Note, __get_dynamic_array_len() returns the total allocated
+ * length of the dynamic array; __print_array() expects the second
+ * parameter to be the number of elements. To get that, the array length
+ * needs to be divided by the element size.
*
* For __string(foo, bar) use __get_str(foo)
*
@@ -288,7 +291,7 @@ TRACE_EVENT(foo_bar,
* This prints out the array that is defined by __array in a nice format.
*/
__print_array(__get_dynamic_array(list),
- __get_dynamic_array_len(list),
+ __get_dynamic_array_len(list) / sizeof(int),
sizeof(int)),
__get_str(str), __get_bitmask(cpus))
);
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