Re: Oops caused by race between livepatch and ftrace

[Steven Rostedt]

On Tue, 21 May 2019 09:16:29 -0500
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> > Hmm, this may blow up with lockdep, as I believe we already have a
> > locking dependency of:
> > 
> >  text_mutex -> ftrace_lock
> > 
> > And this will reverses it. (kprobes appears to take the locks in this
> > order).
> > 
> > Perhaps have live kernel patching grab ftrace_lock?  
> 
> Where does kprobes call into ftrace with the text_mutex?  I couldn't
> find it.

Hmm, maybe it doesn't. I was looking at the arm_kprobe_ftrace() but
it doesn't call it with text_mutex().

Maybe it is fine, but we had better perform a lot of testing with
lockdep on to make sure.

-- Steve