On Mon, Jan 07, 2019 at 04:28:33PM -0500, Steven Rostedt wrote: > On Mon, 7 Jan 2019 22:19:04 +0100 > Andrea Righi <righi.and...@gmail.com> wrote: > > > > > If we put a kretprobe to raw_spin_lock_irqsave() it looks like > > > > kretprobe is going to call kretprobe... > > > > > > Right, but we should be able to add some recursion protection to stop > > > that. I have similar protection in the ftrace code. > > > > If we assume that __raw_spin_lock/unlock*() are always inlined a > > I wouldn't assume that. > > > possible way to prevent this recursion could be to use directly those > > functions to do locking from the kretprobe trampoline. > > > > But I'm not sure if that's a safe assumption... if not I'll see if I can > > find a better solution. > > All you need to do is have a per_cpu variable, where you just do: > > preempt_disable_notrace(); > if (this_cpu_read(kprobe_recursion)) > goto out; > this_cpu_inc(kprobe_recursion); > [...] > this_cpu_dec(kprobe_recursion); > out: > preempt_enable_notrace(); > > And then just ignore any kprobes that trigger while you are processing > the current kprobe. > > Something like that. If you want (or if it already happens) replace > preempt_disable() with local_irq_save().
Oh.. definitely much better. I'll work on that and send a new patch. Thanks for the suggestion! -Andrea
