Message-ID: <544DBA03.1010709@intel.com>
Date: Mon, 27 Oct 2014 11:20:35 +0800
From: Ren Qiaowei <qiaowei.ren@intel.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>, x86@kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-ia64@vger.kernel.org, linux-mips@linux-mips.org
Subject: Re: [PATCH v9 05/12] x86, mpx: on-demand kernel allocation of bounds
 tables
References: <1413088915-13428-1-git-send-email-qiaowei.ren@intel.com> <1413088915-13428-6-git-send-email-qiaowei.ren@intel.com> <alpine.DEB.2.11.1410241257300.5308@nanos>
In-Reply-To: <alpine.DEB.2.11.1410241257300.5308@nanos>
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On 10/24/2014 08:08 PM, Thomas Gleixner wrote:
> On Sun, 12 Oct 2014, Qiaowei Ren wrote:
>> +	/*
>> +	 * Go poke the address of the new bounds table in to the
>> +	 * bounds directory entry out in userspace memory.  Note:
>> +	 * we may race with another CPU instantiating the same table.
>> +	 * In that case the cmpxchg will see an unexpected
>> +	 * 'actual_old_val'.
>> +	 */
>> +	ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
>> +					   expected_old_val, bt_addr);
>
> This is fully preemptible non-atomic context, right?
>
> So this wants a proper comment, why using
> user_atomic_cmpxchg_inatomic() is the right thing to do here.
>

Well, we will address it.

Thanks,
Qiaowei
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