tree 83d949e151f2f7e4a980396538cc0f2356bacfd4
parent 8965593e41dd2d0e2a2f1e6f245336005ea94a2c
author Liu Bo <liubo2009@cn.fujitsu.com> 1321321686 -0500
committer Chris Mason <chris.mason@oracle.com> 1321368808 -0500

Btrfs: fix tree corruption after multi-thread snapshots and inode_cache flush

The btrfs snapshotting code requires that once a root has been
snapshotted, we don't change it during a commit.

But there are two cases to lead to tree corruptions:

1) multi-thread snapshots can commit serveral snapshots in a transaction,
   and this may change the src root when processing the following pending
   snapshots, which lead to the former snapshots corruptions;

2) the free inode cache was changing the roots when it root the cache,
   which lead to corruptions.

This fixes things by making sure we force COW the block after we create a
snapshot during commiting a transaction, then any changes to the roots
will result in COW, and we get all the fs roots and snapshot roots to be
consistent.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>