linux-kernel - Re: [BUGFIX PATCH] kprobes/x86: Remove IRQ disabling from jprobe handlers

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Message-Id: <20171004230804.9427341c928923a196c2a2b5@kernel.org>
Date:   Wed, 4 Oct 2017 23:08:04 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     mingo@...hat.com, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexei Starovoitov <ast@...com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [BUGFIX PATCH] kprobes/x86: Remove IRQ disabling from jprobe
 handlers

On Wed, 4 Oct 2017 12:41:01 +0200
Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Hmm, actually we can not disable jprobe, that has no separate Kconfig.
> > So we need to introduce new kconfig for that.
> > 
> > And, there are several network protocols using jprobe to trace events.
> > (e.g. NET_DCCPPROBE and NET_TCPPROBE)
> > I think they need to migrate to trace-event at first.
> > 
> > So, how about below idea?
> > 
> > 1. Introduce CONFIG_JPROBE_API which only separate jprobe general parts
> >      (no arch dependent code involves) and make it default n.
> > 2. Mark break_handler and jprobe APIs deprecated so that no new user comes up.
> > 3. migrate in-kernel jprobe user to trace-event or ftrace.
> >    (may take some time)
> 
> So my suggestion would be to just return from register_jprobe() and don't register 
> anything.

with CONFIG_JPROBE_API=n, is that right?

> Yes, there are usecases of jprobes in the kernel, but they all look 
> pretty ancient and unused.

Hmm, in that case, should we also remove those users? If we disable such way
those features are just useless.

> 
> So let's try this for -next and see whether anyone has a real usecase. And no 
> Kconfig and deprecation messages - those don't really work in practice - just 
> disable the functionality and force people to (trivially) modify the source if 
> they want to re-enable it.

So you mean I don't have to change those usecases, just let them do.

> 
> If this is fine for a single release then we can just remove it all:
> 
> > 4. after that, we can completely remove jprobe which will be a series for
> >    all archs. (or just one big patch?)
> 
> we want a series of patches - but that's for later.

OK :)

Thank you,

> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@...nel.org>