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Subject[PATCH 4.14 085/193] ext4: prevent data corruption with inline data + DAX
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ross Zwisler <ross.zwisler@linux.intel.com>

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>

---
fs/ext4/inline.c | 10 ----------
fs/ext4/super.c | 5 +++++
2 files changed, 5 insertions(+), 10 deletions(-)

--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -302,11 +302,6 @@ static int ext4_create_inline_data(handl
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_nolo
}
}
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);
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3708,6 +3708,11 @@ static int ext4_fill_super(struct super_
}

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;

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