[ 3.8.y.z extended stable ] Patch "Btrfs: only do the tree_mod_log_free_eb if this is our last ref" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    Btrfs: only do the tree_mod_log_free_eb if this is our last ref

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 5f9a03cddbea2363e3e591605501060aacdc9352 Mon Sep 17 00:00:00 2001
From: Josef Bacik <jbacik at fusionio.com>
Date: Mon, 1 Jul 2013 16:10:16 -0400
Subject: Btrfs: only do the tree_mod_log_free_eb if this is our last ref

commit 7fb7d76f96bfcbea25007d190ba828b18e13d29d upstream.

There is another bug in the tree mod log stuff in that we're calling
tree_mod_log_free_eb every single time a block is cow'ed.  The problem with this
is that if this block is shared by multiple snapshots we will call this multiple
times per block, so if we go to rewind the mod log for this block we'll BUG_ON()
in __tree_mod_log_rewind because we try to rewind a free twice.  We only want to
call tree_mod_log_free_eb if we are actually freeing the block.  With this patch
I no longer hit the panic in __tree_mod_log_rewind.  Thanks,

Reviewed-by: Jan Schmidt <list.btrfs at jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik at fusionio.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/btrfs/ctree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 7a11fb7..d24e546 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1049,7 +1049,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
 		btrfs_set_node_ptr_generation(parent, parent_slot,
 					      trans->transid);
 		btrfs_mark_buffer_dirty(parent);
-		tree_mod_log_free_eb(root->fs_info, buf);
+		if (last_ref)
+			tree_mod_log_free_eb(root->fs_info, buf);
 		btrfs_free_tree_block(trans, root, buf, parent_start,
 				      last_ref);
 	}
--
1.8.1.2