Commit 713cb650 authored Oct 12, 2017 by Ross Zwisler Committed by Greg Kroah-Hartman Nov 30, 2017

ext4: prevent data corruption with inline data + DAX

commit 559db4c6d784ceedc2a5418ced4d357cb843e221 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b891e716

fs/ext4/inline.c

+0 −10

Original line number	Diff line number	Diff line
		@@ -302,11 +302,6 @@ 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);

		@@ -451,11 +446,6 @@ 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);

fs/ext4/super.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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;