linux-kernel - Re: [PATCH]Fix the order of atomic operations in restore_previous

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Date:	Tue, 22 Jan 2008 09:07:46 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	ia64 <linux-ia64@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: [PATCH]Fix the order of atomic operations in
	restore_previous_kprobes on ia64


On Sat, 2008-01-19 at 00:20 +0800, Masami Hiramatsu wrote:
> From: Masami Hiramatsu <mhiramat@...hat.com>
> 
> Fix the order of atomic operations to prevent overwriting
> prev_kprobe[0].
> To pop values from stack, we must decrement stack index right AFTER
> reading values.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> ---
> Details of this issue was reported to
> http://sources.redhat.com/bugzilla/show_bug.cgi?id=2071
> 
>    arch/ia64/kernel/kprobes.c |    7 ++++---
>    1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Index: 2.6.24-rc8/arch/ia64/kernel/kprobes.c
> ===================================================================
> --- 2.6.24-rc8.orig/arch/ia64/kernel/kprobes.c  2008-01-17
> 21:14:01.000000000 -0500
> +++ 2.6.24-rc8/arch/ia64/kernel/kprobes.c       2008-01-17
> 21:14:01.000000000 -0500
> @@ -381,9 +381,10 @@
>    static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk
> *kcb)
>    {
>         unsigned int i;
> -       i = atomic_sub_return(1, &kcb->prev_kprobe_index);
> -       __get_cpu_var(current_kprobe) = kcb->prev_kprobe[i].kp;
> -       kcb->kprobe_status = kcb->prev_kprobe[i].status;
> +       i = atomic_read(&kcb->prev_kprobe_index);
> +       __get_cpu_var(current_kprobe) = kcb->prev_kprobe[i-1].kp;
> +       kcb->kprobe_status = kcb->prev_kprobe[i-1].status;
> +       atomic_sub(1, &kcb->prev_kprobe_index);
>    }
> 
>    static void __kprobes set_current_kprobe(struct kprobe *p,
Acked. Thanks for the patch.

Thanks,
Shaohua

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