From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH] Introduce a method to catch mmap_region (was: Recent
 kernel "mount" slow)
Date: Thu, 29 Nov 2012 06:30:43 +0000
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Cc: Mikulas Patocka <mpatocka@redhat.com>,
	Jens Axboe <axboe@kernel.dk>,
	Jeff Chua <jeff.chua.linux@gmail.com>,
	Lai Jiangshan <laijs@cn.fujitsu.com>, Jan Kara <jack@suse.cz>,
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	linux-fsdevel <linux-fsdevel@vger.kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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On Thu, Nov 29, 2012 at 06:25:19AM +0000, Al Viro wrote:

> 	Umm...  set_blocksize() is calling kill_bdev(), which does
> truncate_inode_pages(mapping, 0).  What's going to happen to data in
> the dirty pages?  IO in progress is not the only thing to worry about...

Note that sync_blockdev() a few lines prior to that is good only if we
have no other processes doing write(2) (or dirtying the mmapped pages,
for that matter).  The window isn't too wide, but...