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Date: Tue, 3 Oct 2017 11:33:44 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: mingo@redhat.com, x86@kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Alexei Starovoitov <ast@kernel.org>, Alexei Starovoitov <ast@fb.com>
Subject: Re: [BUGFIX PATCH] kprobes/x86: Remove IRQ disabling from jprobe
 handlers
Message-ID: <20171003093344.feh7gqa4aimsjwqv@gmail.com>
References: <20170930231251.emiuyrapdgzpcylp@inn>
 <150701508194.32266.14458959863314097305.stgit@devbox>
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* Masami Hiramatsu <mhiramat@kernel.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@kernel.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?

Thanks,

	Ingo