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ext4: prevent data corruption with inline data + DAX

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If an inode has inline data it is currently prevented from using DAX by a
check in ext4_set_inode_flags().  When the inode grows inline data via
ext4_create_inline_data() or removes its inline data via
ext4_destroy_inline_data_nolock(), the value of S_DAX can change.

Currently these changes are unsafe because we don't hold off page faults
and I/O, write back dirty radix tree entries and invalidate all mappings.
There are also issues with mm-level races when changing the value of S_DAX,
as well as issues with the VM_MIXEDMAP flag:

https://www.spinics.net/lists/linux-xfs/msg09859.html

The unsafe transition of S_DAX can reliably cause data corruption, as shown
by the following fstest:

https://patchwork.kernel.org/patch/9948381/

Fix this issue by preventing the DAX mount option from being used on
filesystems that were created to support inline data.  Inline data is an
option given to mkfs.ext4.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
CC: stable@vger.kernel.org
This commit is contained in:
Ross Zwisler 2017-10-12 11:52:34 -04:00 committed by Theodore Ts'o
parent 51e3ae81ec
commit 559db4c6d7
2 changed files with 5 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/ext4/inline.c
View File

@ -303,11 +303,6 @@ static int ext4_create_inline_data(handle_t *handle,
EXT4_I(inode)->i_inline_size = len + EXT4_MIN_INLINE_DATA_SIZE;
ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
ext4_set_inode_flag(inode, EXT4_INODE_INLINE_DATA);
/*
* Propagate changes to inode->i_flags as well - e.g. S_DAX may
* get cleared
*/
ext4_set_inode_flags(inode);
get_bh(is.iloc.bh);
error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
@ -452,11 +447,6 @@ static int ext4_destroy_inline_data_nolock(handle_t *handle,
}
}
ext4_clear_inode_flag(inode, EXT4_INODE_INLINE_DATA);
/*
* Propagate changes to inode->i_flags as well - e.g. S_DAX may
* get set.
*/
ext4_set_inode_flags(inode);
get_bh(is.iloc.bh);
error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);

5
fs/ext4/super.c
View File

@ -3708,6 +3708,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
}
if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
if (ext4_has_feature_inline_data(sb)) {
ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
" that may contain inline data");
goto failed_mount;
}
err = bdev_dax_supported(sb, blocksize);
if (err)
goto failed_mount;