ext4: prevent data corruption with inline data + DAX

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

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index f0bbc8c..1367553 100644 (file)
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -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);

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b104096..986475c 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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;