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authorLiu Bo <liubo2009@cn.fujitsu.com>2011-11-14 20:48:06 -0500
committerChris Mason <chris.mason@oracle.com>2011-11-15 09:53:28 -0500
commitf1ebcc74d5b2159f44c96b479b6eb8afc7829095 (patch)
tree83d949e151f2f7e4a980396538cc0f2356bacfd4
parent8965593e41dd2d0e2a2f1e6f245336005ea94a2c (diff)
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>
-rw-r--r--fs/btrfs/ctree.c17
-rw-r--r--fs/btrfs/ctree.h2
-rw-r--r--fs/btrfs/transaction.c8
3 files changed, 26 insertions, 1 deletions
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0fe615e4ea3..dede441bdee 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -514,10 +514,25 @@ static inline int should_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf)
{
+ /* ensure we can see the force_cow */
+ smp_rmb();
+
+ /*
+ * We do not need to cow a block if
+ * 1) this block is not created or changed in this transaction;
+ * 2) this block does not belong to TREE_RELOC tree;
+ * 3) the root is not forced COW.
+ *
+ * What is forced COW:
+ * when we create snapshot during commiting the transaction,
+ * after we've finished coping src root, we must COW the shared
+ * block to ensure the metadata consistency.
+ */
if (btrfs_header_generation(buf) == trans->transid &&
!btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN) &&
!(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
- btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
+ btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)) &&
+ !root->force_cow)
return 0;
return 1;
}
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index b9ba59ff929..b1cb3c05248 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1271,6 +1271,8 @@ struct btrfs_root {
* for stat. It may be used for more later
*/
dev_t anon_dev;
+
+ int force_cow;
};
struct btrfs_ioctl_defrag_range_args {
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 6a0574e923b..81376d94cd3 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -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;