Re: [PATCH 2/2] perf probe: Fix offline module name missmatch issue

Masami Hiramatsu
2016-04-26T14:46:02Z

On Tue, 26 Apr 2016 19:55:41 +0530
Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> wrote:

> Perf can add a probe on kernel module which has not been loaded yet.
> Current implementation finds module name from path. But if filename
> is different from actual module name then perf fails to register
> probe while loading module because of mismatch in 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
>

Looks good to me :)

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you!

> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.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 d58de20..26803e1 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -642,32 +642,23 @@ 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;
> }
>
> --
> 1.9.1
>

--
Masami Hiramatsu <mhiramat@kernel.org>