Hi Andrea and Steve, On Mon, 7 Jan 2019 22:34:39 +0100 Andrea Righi <[email protected]> wrote:
> On Mon, Jan 07, 2019 at 04:28:33PM -0500, Steven Rostedt wrote: > > On Mon, 7 Jan 2019 22:19:04 +0100 > > Andrea Righi <[email protected]> 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! Thank you for pointing it out, Since we already have current_kprobe per_cpu, it can be done by setting up a dummy kprobe on it. I'll add that in v2 series. Actually, this bug has been introduced a long time ago by me... when I introduced asm-coded kretprobe-trampoline. Before that, kretprobe trampoline handler uses a kprobe to hook it, so the 2nd kretprobe must be skipped automatically. Thank you, -- Masami Hiramatsu <[email protected]>
