linux-kernel - Re: [RFC PATCH -tip 0/5] kprobes: Abolish jprobe APIs

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Message-ID: <20171009141054.7b9c0686@gandalf.local.home>
Date:   Mon, 9 Oct 2017 14:10:54 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jonathan Corbet <corbet@....net>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Ian McDonald <ian.mcdonald@...di.co.nz>,
        Vlad Yasevich <vyasevich@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [RFC PATCH -tip 0/5] kprobes: Abolish jprobe APIs

On Mon, 9 Oct 2017 09:33:50 -0600
Jonathan Corbet <corbet@....net> wrote:

> >       will prevent the callback from being called again. But this wrapper
> >       adds some overhead, and if the callback is safe from recursion,
> >       it can set this flag to disable the ftrace protection.  
> 
> What happens if you mark a function safe and it recurses anyway?  Say, if
> somebody else has hooked a different function unknown to the current
> caller? 

Oh, if another callback is attached to a function that gets called
within this function, that is fine. In fact I do that all the time. The
problem is if the callback gets called again and then goes into a
recursive loop.

-- Steve