From: Dmitry Monakhov <dmonakhov@openvz.org>
Date: Sat, 29 Sep 2012 04:55:23 +0000 (-0400)
Subject: ext4: serialize unlocked dio reads with truncate
X-Git-Tag: v3.7-rc1~91^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1c9114f9c0f10f58dd7e568a7152025af47b27e5;p=pandora-kernel.git

ext4: serialize unlocked dio reads with truncate

Current serialization will works only for DIO which holds
i_mutex, but nonlocked DIO following race is possible:

dio_nolock_read_task            truncate_task
				->ext4_setattr()
				 ->inode_dio_wait()
->ext4_ext_direct_IO
  ->ext4_ind_direct_IO
    ->__blockdev_direct_IO
      ->ext4_get_block
				 ->truncate_setsize()
				 ->ext4_truncate()
				 #alloc truncated blocks
				 #to other inode
      ->submit_io()
     #INFORMATION LEAK

In order to serialize with unlocked DIO reads we have to
rearrange wait sequence
1) update i_size first
2) if i_size about to be reduced wait for outstanding DIO requests
3) and only after that truncate inode blocks

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---

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