Subject: RE: [PATCH 2/2] hugetlb: synchronize alloc with page cache insert
From: Adam Litke <agl@us.ibm.com>
To: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Cc: William Lee Irwin III <wli@holomorphy.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
In-Reply-To: <200601121907.k0CJ7og16283@unix-os.sc.intel.com>
References: <200601121907.k0CJ7og16283@unix-os.sc.intel.com>
Content-Type: text/plain
Organization: IBM
Date: Thu, 12 Jan 2006 13:48:59 -0600
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On Thu, 2006-01-12 at 11:07 -0800, Chen, Kenneth W wrote:
> Sorry, I don't think patch 1 by itself is functionally correct.  It opens
> a can of worms with race window all over the place.  It does more damage
> than what it is trying to solve.  Here is one case:
> 
> 1 thread fault on hugetlb page, allocate a non-zero page, insert into the
> page cache, then proceed to zero it.  While in the middle of the zeroing,
> 2nd thread comes along fault on the same hugetlb page.  It find it in the
> page cache, went ahead install a pte and return to the user.  User code
> modify some parts of the hugetlb page while the 1st thread is still
> zeroing.  A potential silent data corruption.

I don't think the above case is possible because of find_lock_page().
The second thread would wait on the page to be unlocked by the thread
zeroing it before it could proceed.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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