linux-ext4 - [PATCH] ext4: serialize unlocked dio reads with truncate

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Message-Id: <1346690448-16917-1-git-send-email-dmonakhov@openvz.org>
Date:	Mon,  3 Sep 2012 20:40:48 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	linux-ext4@...r.kernel.org
Cc:	tytso@....edu, Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH] ext4: serialize unlocked dio reads with truncate

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

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
rearange wait sequance
1) update i_size first
2) wait for outstanding DIO requests
3) and only after that truncate inode blocks

Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
---
 fs/ext4/inode.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d12d30e..ee534ab 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4304,8 +4304,6 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 	}
 
 	if (attr->ia_valid & ATTR_SIZE) {
-		inode_dio_wait(inode);
-
 		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
 			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
@@ -4355,6 +4353,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 	if (attr->ia_valid & ATTR_SIZE) {
 		if (attr->ia_size != i_size_read(inode))
 			truncate_setsize(inode, attr->ia_size);
+		inode_dio_wait(inode);
 		ext4_truncate(inode);
 	}
 
-- 
1.7.7.6

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