Patch "ext4: unmap metadata when zeroing blocks" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

ext4: unmap metadata when zeroing blocks

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-unmap-metadata-when-zeroing-blocks.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Fri, 30 Sep 2016 02:02:29 -0400
Subject: ext4: unmap metadata when zeroing blocks

From: Jan Kara <[email protected]>

commit 9b623df614576680cadeaa4d7e0b5884de8f7c17 upstream.

When zeroing blocks for DAX allocations, we also have to unmap aliases in the block device mappings. Otherwise writeback can overwrite zeros with stale data from block device page cache.

---
 fs/ext4/inode.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

@@ -647,11 +647,19 @@ found:
 		/*
 		 * We have to zeroout blocks before inserting them into extent
 		 * status tree. Otherwise someone could look them up there and
-		 * use them before they are really zeroed.
+		 * use them before they are really zeroed. We also have to
+		 * unmap metadata before zeroing as otherwise writeback can
+		 * overwrite zeros with stale data from block device.
 		 */
 		if (flags & EXT4_GET_BLOCKS_ZERO &&
 		    map->m_flags & EXT4_MAP_MAPPED &&
 		    map->m_flags & EXT4_MAP_NEW) {
+			ext4_lblk_t i;
+
+			for (i = 0; i < map->m_len; i++) {
+				unmap_underlying_metadata(inode->i_sb->s_bdev,
+							  map->m_pblk + i);
+			}
 			ret = ext4_issue_zeroout(inode, map->m_lblk,
 						 map->m_pblk, map->m_len);
 			if (ret) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/ext4-allow-dax-writeback-for-hole-punch.patch queue-4.8/mm-filemap-don-t-plant-shadow-entries-without-radix-tree-node.patch queue-4.8/reiserfs-unlock-superblock-before-calling-reiserfs_quota_on_mount.patch queue-4.8/ext4-unmap-metadata-when-zeroing-blocks.patch queue-4.8/jbd2-fix-lockdep-annotation-in-add_transaction_credits.patch