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

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Message-ID: <47D57D28.7070100@redhat.com>
Date:	Mon, 10 Mar 2008 14:25:44 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Shaohua Li <shaohua.li@...el.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

Hello Shaohua,

Thank you for reviewing!

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

You are correct. I'll fix that.

> 
>> +       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?

I think that other cpu never change the flag, because the caller of this
function(__register_kprobe) locks kprobe_mutex in kernel/kprobes.c.

> Thanks,
> Shaohua

Thanks,

-- 
Masami Hiramatsu

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

e-mail: mhiramat@...hat.com

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