Signed-off-by: Liu Bo <liubo2...@cn.fujitsu.com>
---
fs/btrfs/ctree.c | 17 ++++++++++++++++-
fs/btrfs/ctree.h | 2 ++
fs/btrfs/transaction.c | 8 ++++++++
3 files changed, 26 insertions(+), 1 deletions(-)
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 4a96337..2b38acd 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -571,10 +571,25 @@ 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->transaction->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 346ad08..a635f1c 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 e31cdef..ee3db16 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -784,6 +784,10 @@ 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;
--
1.6.5.2
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