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SubjectRe: [PATCH] tracing/profile: Fix profile_disable vs module_unload
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On Mon, 2009-08-24 at 12:19 +0800, Li Zefan wrote:
> If the correspoding module is unloaded before ftrace_profile_disable()
> is called, event->profile_disable() won't be called, which can
> cause oops:
>
> # insmod trace-events-sample.ko
> # perf record -f -a -e sample:foo_bar sleep 3 &
> # sleep 1
> # rmmod trace_events_sample
> # insmod trace-events-sample.ko
> OOPS!
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>


Hrmm, feel fragile, why don't we check if all a modules tracepoints are
unused on unload?

> ---
> kernel/trace/trace_event_profile.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/trace/trace_event_profile.c b/kernel/trace/trace_event_profile.c
> index 11ba5bb..55a25c9 100644
> --- a/kernel/trace/trace_event_profile.c
> +++ b/kernel/trace/trace_event_profile.c
> @@ -5,6 +5,7 @@
> *
> */
>
> +#include <linux/module.h>
> #include "trace.h"
>
> int ftrace_profile_enable(int event_id)
> @@ -14,7 +15,8 @@ int ftrace_profile_enable(int event_id)
>
> mutex_lock(&event_mutex);
> list_for_each_entry(event, &ftrace_events, list) {
> - if (event->id == event_id && event->profile_enable) {
> + if (event->id == event_id && event->profile_enable &&
> + try_module_get(event->mod)) {
> ret = event->profile_enable(event);
> break;
> }
> @@ -32,6 +34,7 @@ void ftrace_profile_disable(int event_id)
> list_for_each_entry(event, &ftrace_events, list) {
> if (event->id == event_id) {
> event->profile_disable(event);
> + module_put(event->mod);
> break;
> }
> }


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