Commit 1c9114f9 authored Sep 29, 2012 by Dmitry Monakhov Committed by Theodore Ts'o Sep 29, 2012

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>

parent 17335dcc

fs/ext4/inode.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -4283,7 +4283,6 @@ 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);
		@@ -4332,8 +4331,12 @@ int ext4_setattr(struct dentry dentry, struct iattr attr)
		}

		if (attr->ia_valid & ATTR_SIZE) {
		if (attr->ia_size != i_size_read(inode))
		if (attr->ia_size != i_size_read(inode)) {
		truncate_setsize(inode, attr->ia_size);
		/* Inode size will be reduced, wait for dio in flight */
		if (orphan)
		inode_dio_wait(inode);
		}
		ext4_truncate(inode);
		}

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