[tip:perf/core] perf probe: Fix offline module name missmatch issue

tip-bot for Ravi Bangoria
2016-04-27T15:39:03Z

Commit-ID: 63a29613d7c69f17b6a3266bfc338986698b2546
Gitweb: http://git.kernel.org/tip/63a29613d7c69f17b6a3266bfc338986698b2546
Author: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
AuthorDate: Tue, 26 Apr 2016 19:55:41 +0530
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 26 Apr 2016 13:15:01 -0300

perf probe: Fix offline module name missmatch issue

Perf can add a probe on kernel module which has not been loaded yet.

The current implementation finds the module name from path. But if the
filename is different from the actual module name then perf fails to
register a probe while loading module because of mismatch in the names.

For example, samples/kobject/kobject-example.ko is loaded as
kobject_example.

Before applying patch:

$ sudo ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in kobject-example)

You can now use it in all perf tools, such as:

perf record -e probe:foo_show -aR sleep 1

$ cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show kobject-example:foo_show

$ insmod kobject-example.ko

$ lsmod
Module Size Used by
kobject_example 16384 0

Generate read to /sys/kernel/kobject_example/foo while recording data
with below command
$ sudo ./perf record -e probe:foo_show -a
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.093 MB perf.data ]

$./perf report --stdio -F overhead,comm,dso,sym
Error:
The perf.data.old file has no samples!

After applying patch:

$ sudo ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in kobject_example)

You can now use it in all perf tools, such as:

perf record -e probe:foo_show -aR sleep 1

$ sudo cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show kobject_example:foo_show

$ insmod kobject-example.ko

$ lsmod
Module Size Used by
kobject_example 16384 0

Generate read to /sys/kernel/kobject_example/foo while recording data
with below command
$ sudo ./perf record -e probe:foo_show -a
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.097 MB perf.data (8 samples) ]

$ sudo ./perf report --stdio -F overhead,comm,dso,sym
...
# Samples: 8 of event 'probe:foo_show'
# Event count (approx.): 8
#
# Overhead Command Shared Object Symbol
# ........ ....... ................. ............
#
100.00% cat [kobject_example] [k] foo_show

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1461680741-12517-2-git-send-email-ravi.bangoria@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/probe-event.c | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 0de5d10..bc2eb7c 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -588,32 +588,23 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
int ntevs, const char *module)
{
int i, ret = 0;
- char *tmp;
+ char *mod_name = NULL;

if (!module)
return 0;

- tmp = strrchr(module, '/');
- if (tmp) {
- /* This is a module path -- get the module name */
- module = strdup(tmp + 1);
- if (!module)
- return -ENOMEM;
- tmp = strchr(module, '.');
- if (tmp)
- *tmp = '\0';
- tmp = (char *)module; /* For free() */
- }
+ mod_name = find_module_name(module);

for (i = 0; i < ntevs; i++) {
- tevs[i].point.module = strdup(module);
+ tevs[i].point.module =
+ strdup(mod_name ? mod_name : module);
if (!tevs[i].point.module) {
ret = -ENOMEM;
break;
}
}

- free(tmp);
+ free(mod_name);
return ret;
}