Patch "btrfs: skip waiting on ordered range for special files" has been added to the 3.10-stable tree

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

btrfs: skip waiting on ordered range for special files

to the 3.10-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:
btrfs-skip-waiting-on-ordered-range-for-special-files.patch
and it can be found in the queue-3.10 subdirectory.

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

From: Jeff Mahoney <[email protected]>
Date: Fri, 11 Sep 2015 21:44:17 -0400
Subject: btrfs: skip waiting on ordered range for special files

From: Jeff Mahoney <[email protected]>

commit a30e577c96f59b1e1678ea5462432b09bf7d5cbc upstream.

In btrfs_evict_inode, we properly truncate the page cache for evicted inodes but then we call btrfs_wait_ordered_range for every inode as well. It's the right thing to do for regular files but results in incorrect behavior for device inodes for block devices.

filemap_fdatawrite_range gets called with inode->i_mapping which gets resolved to the block device inode before getting passed to wbc_attach_fdatawrite_inode and ultimately to inode_to_bdi. What happens next depends on whether there's an open file handle associated with the inode. If there is, we write to the block device, which is unexpected behavior. If there isn't, we through normally and inode->i_data is used. We can also end up racing against open/close which can result in crashes when i_mapping points to a block device inode that has been closed.

Since there can't be any page cache associated with special file inodes, it's safe to skip the btrfs_wait_ordered_range call entirely and avoid the problem.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=100911

---
 fs/btrfs/inode.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -4650,7 +4650,8 @@ void btrfs_evict_inode(struct inode *ino
 		goto no_delete;
 	}
 	/* do we really want it for ->i_nlink > 0 and zero btrfs_root_refs? */
-	btrfs_wait_ordered_range(inode, 0, (u64)-1);
+	if (!special_file(inode->i_mode))
+		btrfs_wait_ordered_range(inode, 0, (u64)-1);
 
 	if (root->fs_info->log_root_recovering) {
 		BUG_ON(test_bit(BTRFS_INODE_HAS_ORPHAN_ITEM,

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

queue-3.10/btrfs-skip-waiting-on-ordered-range-for-special-files.patch