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    SubjectRe: [PATCH 01/18] tracing: Add function based events
    On Mon, 5 Feb 2018 10:00:50 -0500
    Steven Rostedt <rostedt@goodmis.org> wrote:

    > On Mon, 5 Feb 2018 09:24:23 +0100
    > Jiri Olsa <jolsa@redhat.com> wrote:
    >
    >
    > > should this be done under 'func_event_mutex' ?
    >
    > Probably.

    I think we only need to add the list.

    >
    > >
    > > I tried and crashed the system by running 2 scripts with:
    > >
    > > echo 'ip_rcv(u64 skb, u64 dev)' > /sys/kernel/debug/tracing/function_events
    > > echo 'SyS_openat(int dfd, string buf, x32 flags, x32 mode)' >> /sys/kernel/debug/tracing/function_events
    > > echo 'SyS_open(x8[32] buf, x32 flags, x32 mode)' >> /sys/kernel/debug/tracing/function_events
    > >
    >

    There's no reason that we can't have more than one function event
    attached to the same function. I'm adding this:

    diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
    index b145639eac45..928168fc2025 100644
    --- a/kernel/trace/trace_event_ftrace.c
    +++ b/kernel/trace/trace_event_ftrace.c
    @@ -1275,12 +1275,6 @@ static int create_function_event(int argc, char **argv)
    if (state != FUNC_STATE_END)
    goto fail;

    - ret = -EALREADY;
    - list_for_each_entry(fe, &func_events, list) {
    - if (strcmp(fe->func, func_event->func) == 0)
    - goto fail;
    - }
    -
    ret = ftrace_set_filter(&func_event->ops, func_event->func,
    strlen(func_event->func), 0);
    if (ret < 0)
    @@ -1290,7 +1284,9 @@ static int create_function_event(int argc, char **argv)
    if (ret < 0)
    goto fail;

    + mutex_lock(&func_event_mutex);
    list_add_tail(&func_event->list, &func_events);
    + mutex_unlock(&func_event_mutex);
    return 0;
    fail:
    free_func_event(func_event);
    -- Steve

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