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

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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>
This commit is contained in:
Liu Bo
2011-11-14 20:48:06 -05:00
committed by Chris Mason
parent 8965593e41
commit f1ebcc74d5
3 changed files with 26 additions and 1 deletions
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8
fs/btrfs/transaction.c
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@@ -785,6 +785,10 @@ static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
btrfs_save_ino_cache(root, trans);
/* see comments in should_cow_block() */
root->force_cow = 0;
smp_wmb();
if (root->commit_root != root->node) {
mutex_lock(&root->fs_commit_mutex);
switch_commit_root(root);
@@ -947,6 +951,10 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
btrfs_tree_unlock(old);
free_extent_buffer(old);
/* see comments in should_cow_block() */
root->force_cow = 1;
smp_wmb();
btrfs_set_root_node(new_root_item, tmp);
/* record when the snapshot was created in key.offset */
key.offset = trans->transid;