linux-ext4 - question about punch hole

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Date:	Fri, 26 Aug 2011 10:53:27 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: question about punch hole

Hi Allison,

Currently, punch hole flushes all pages to disk and releases pages in
page cache, and then calls ext4_ext_map_blocks.

Assume that if a new page in the punching's range is mapped after
releasing pages and before down_write i_data_sem,
then ext4_ext_map_blocks will release map info of the page in extent
tree.  However, up layers does not know this, and they think the page
is mapped.

I can not find how punch hole handle the situation above.  Could you
shed a light on it?

-- 
Best Wishes
Yongqiang Yang
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