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

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Message-ID: <20171003171100.p535ul3wml4uhsow@gmail.com>
Date:   Tue, 3 Oct 2017 19:11:00 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...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


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Tue, 3 Oct 2017 11:33:44 +0200
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > 
> > > Jprobe actually doesn't need to disable IRQs while calling
> > > handlers, because Documentation/kprobes.txt says:
> > > 
> > > -----
> > >  Probe handlers are run with preemption disabled.  Depending on the
> > >  architecture and optimization state, handlers may also run with
> > >  interrupts disabled (e.g., kretprobe handlers and optimized kprobe
> > >  handlers run without interrupt disabled on x86/x86-64).
> > > -----
> > > 
> > > So let's remove IRQ disabling from jprobes too.
> > > 
> > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > > ---
> > >  arch/x86/kernel/kprobes/core.c |    2 --
> > >  1 file changed, 2 deletions(-)
> > > 
> > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > > index b48e0efd668e..bd36f3c33cd0 100644
> > > --- a/arch/x86/kernel/kprobes/core.c
> > > +++ b/arch/x86/kernel/kprobes/core.c
> > > @@ -1099,8 +1099,6 @@ int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
> > >  	 * raw stack chunk with redzones:
> > >  	 */
> > >  	__memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr, MIN_STACK_SIZE(addr));
> > > -	regs->flags &= ~X86_EFLAGS_IF;
> > > -	trace_hardirqs_off();
> > >  	regs->ip = (unsigned long)(jp->entry);
> > >  
> > >  	/*
> > 
> > Could you please also do a patch that disables jprobes permanently, in preparation 
> > of eventually removing them later?
> 
> Would you mean introducing CONFIG_JPROBE_API and cut APIs out,
> or just adding "__deprecated" for each API?

No, I'd suggest removing in-kernel uses and disabling jprobes in the Kconfig 
altogether, but without removing the code and its integration for the time being.

Thanks,

	Ingo