On Tue, 21 Jan 2020 19:29:05 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Thu, 16 Jan 2020 23:44:52 +0900 > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > Since the 5 jiffies delay for the optimizer is too > > short to wait for other probes, make it longer, > > like 1 second. > > Hi Masami, > > Can you explain more *why* 5 jiffies is too short. Yes, I had introduced this 5 jiffies delay for multiple probe registration and unregistration like systemtap, which will use array-based interface to register/unregister. In that case, 5 jiffies will be enough for the delay to wait for other kprobe registration/unregsitration. However, since perf and ftrace register/unregister probes one-by-one with RCU synchronization interval, the optimizer will be started before finishing to register/unregister all probes. And the optimizer locks kprobe_mutex a while -- RCU-tasks synchronization. Since the kprobe_mutex is also involved in disabling kprobes, this also stops probe-event disabling. Maybe 5 jiffies is enough for adding/removing a few probe events, but not enough for dozens of probe events. Thank you, > > Thanks! > > -- Steve > > > > > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > > --- > > kernel/kprobes.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index 0dacdcecc90f..9c6e230852ad 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > @@ -469,7 +469,8 @@ static int kprobe_optimizer_queue_update; > > > > static void kprobe_optimizer(struct work_struct *work); > > static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer); > > -#define OPTIMIZE_DELAY 5 > > +/* Wait 1 second for starting optimization */ > > +#define OPTIMIZE_DELAY HZ > > > > /* > > * Optimize (replace a breakpoint with a jump) kprobes listed on > -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
