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

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 5 Oct 2017 09:57:04 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > On Wed, 4 Oct 2017 12:41:01 +0200
> > Ingo Molnar <mingo@kernel.org> wrote:
> > 
> > > 
> > > * Masami Hiramatsu <mhiramat@kernel.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?
> 
> No, unconditionally off with a WARN_ON_ONCE() warning in the registry function and 
> the deactivation of all in-kernel uses (such as self-tests).
> 
> The point is to make people that _truly_ rely on it complain - not just make them 
> silently turn on a Kconfig option ...

Hmm, but in that case, anyway we have to remove or rename the function
like register_jprobe. Or would that "unconditionally" mean "#if 0"?

> > > 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.
> 
> My hypothesis is that those features are not used (hence useless), but we should 
> first test whether there's any reliance before we remove code.

Agreed.

Thank you,

> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@kernel.org>