linux-kernel - Re: [PATCH v9 05/12] x86, mpx: on-demand kernel allocation of bounds tables

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Date:	Mon, 27 Oct 2014 11:20:35 +0800
From:	Ren Qiaowei <qiaowei.ren@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, linux-mips@...ux-mips.org
Subject: Re: [PATCH v9 05/12] x86, mpx: on-demand kernel allocation of bounds
 tables

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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