linux-kernel - Re: [PATCH -mm] kprobes: kprobe-booster for ia64

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Date:	Mon, 10 Mar 2008 11:43:20 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	ia64 <linux-ia64@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: [PATCH -mm] kprobes: kprobe-booster for ia64


On Sat, 2008-03-08 at 00:01 +0800, Masami Hiramatsu wrote:
> From: Masami Hiramatsu <mhiramat@...hat.com>
> 

> +
> +/*
> + * In this function, we check whether the target bundle modifies IP
> or
> + * it triggers an exception. If so, it cannot be boostable.
> + */
> +static int __kprobes can_boost(bundle_t *bundle, uint slot,
> +                              unsigned long bundle_addr)
> +{
> +       unsigned int template = bundle->quad0.template;
> +
> +       do {
> +               if (search_exception_tables(bundle_addr + slot) ||
> +                   __is_ia64_break_inst(bundle, slot))
> +                       return 0;       /* exception may occur in this
> bundle*/
> +       } while ((++slot) < 3);
> +       template &= 0x1e;
> +       if (template >= 0x10 /* including B unit */ ||
> +           template == 0x04 /* including X unit */ ||
> +           template == 0x06) /* undefined */
> +               return 0;
> +
> +       return 1;
> +}
> +
> +/* Prepare long jump bundle and disables other boosters if need */
> +static void __kprobes prepare_booster(struct kprobe *p)
> +{
> +       unsigned long addr = (unsigned long)p->addr & ~0xFULL;
> +       unsigned int slot = addr & 0xf;
slot = (unsigned long)p->addr & 0xf ?

> +       struct kprobe *other_kp;
> +
> +       if (can_boost(&p->ainsn.insn[0].bundle, slot, addr)) {
> +               set_brl_inst(&p->ainsn.insn[1].bundle, (bundle_t
> *)addr + 1);
> +               p->ainsn.inst_flag |= INST_FLAG_BOOSTABLE;
> +       }
> +
> +       /* disables boosters in previous slots */
> +       for (; addr < (unsigned long)p->addr; addr++) {
> +               other_kp = get_kprobe((void *)addr);
> +               if (other_kp)
> +                       other_kp->ainsn.inst_flag &=
> ~INST_FLAG_BOOSTABLE;
> +       }
> +}
> +
There is no lock to protect the flag. If one cpu invokes other_kp and
the other cpu is changing the flag, what's the result?

Thanks,
Shaohua

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