linux-kernel - Re: [PATCH 0/2] kprobes: Fix kretprobe incorrect stacking order problem

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Date:   Mon, 7 Jan 2019 14:59:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andrea Righi <righi.andrea@...il.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, peterz@...radead.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] kprobes: Fix kretprobe incorrect stacking order
 problem

On Mon, 7 Jan 2019 20:52:09 +0100
Andrea Righi <righi.andrea@...il.com> wrote:

> > Ug, kretprobe calls spinlocks in the callback? I wonder if we can
> > remove them.
> > 
> > I'm guessing this is a different issue than the one that this patch
> > fixes. This sounds like we are calling kretprobe from kretprobe?
> > 
> > -- Steve  
> 
> kretprobe_trampoline()
>   -> trampoline_handler()
>     -> kretprobe_hash_lock()
>       -> raw_spin_lock_irqsave()  
> 
> 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.

-- Steve