linux-kernel - Re: [PATCH 1/2] x86: fix kprobe

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Date:	Tue, 18 Dec 2007 22:32:28 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>, Ingo Molnar <mingo@...e.hu>
CC:	Roland McGrath <roland@...hat.com>, prasanna@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	Harvey Harrison <harvey.harrison@...il.com>,
	systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 1/2] x86: fix kprobe_handler reenable preemption

Hi

Masami Hiramatsu wrote:
> Fix a preemption bug in kprobe_handler(). It has to call preempt_enable()
> before returning.
> I think this is critical on preemptive kernel.

Sorry, this patch has a mistake.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> ---
>  arch/x86/kernel/kprobes.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: b/arch/x86/kernel/kprobes.c
> ===================================================================
> --- a/arch/x86/kernel/kprobes.c	2007-12-18 12:51:00.000000000 -0500
> +++ b/arch/x86/kernel/kprobes.c	2007-12-18 12:53:38.000000000 -0500
> @@ -467,7 +467,8 @@
>  				arch_disarm_kprobe(p);
>  				regs->ip = (unsigned long)p->addr;
>  				reset_current_kprobe();
> -				return 1;
> +				ret = 1;
> +				goto no_kprobe;
>  #endif
>  			}
>  			/* We have reentered the kprobe_handler(), since
> @@ -481,7 +482,7 @@
>  			kprobes_inc_nmissed_count(p);
>  			prepare_singlestep(p, regs);
>  			kcb->kprobe_status = KPROBE_REENTER;
> -			return 1;
> +			ret = 1;

Here, "return 1;" is correct. After single step is done, preemption is enabled
in post_kprobe_handler().

>  		} else {
>  			if (*addr != BREAKPOINT_INSTRUCTION) {
>  			/* The breakpoint instruction was removed by
> 

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com, masami.hiramatsu.pt@...achi.com

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