From mboxrd@z Thu Jan  1 00:00:00 1970
From: Masami Hiramatsu <mhiramat@redhat.com>
Date: Mon, 10 Mar 2008 18:25:44 +0000
Subject: Re: [PATCH -mm] kprobes: kprobe-booster for ia64
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References: <47D166E7.2050803@redhat.com> <1205120600.20271.3.camel@sli10-desk.sh.intel.com>
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To: Shaohua Li <shaohua.li@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, ia64 <linux-ia64@vger.kernel.org>, "Luck, Tony" <tony.luck@intel.com>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Jim Keniston <jkenisto@us.ibm.com>, systemtap-ml <systemtap@sources.redhat.com>

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@redhat.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@redhat.com