We've suffered some transid mismatches by using sub transid,
here is a case:
before:
parent A (gen = x) parent B(gen = x)
\ /
\ /
\ /
block C (gen = x)
After We can update block C via parent A:
parent A (gen = x + 1) parent B(gen = x)
\ /
\ /
\ /
block C (gen = x + 1)
We'll get a mismatch between parent B and block C.
Fix it by:
COW the block if it can be shared and its gen is not same with sub transid.
Signed-off-by: Liu Bo <liubo2...@cn.fujitsu.com>
---
fs/btrfs/ctree.c | 32 +++++++++++++++++++++-----------
1 files changed, 21 insertions(+), 11 deletions(-)
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 2b38acd..6cc9529 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -575,23 +575,33 @@ static inline int should_cow_block(struct
btrfs_trans_handle *trans,
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.
+ * We should cow a block if
+ * 1) the root is forced COW,
+ * 2) this block has not been updated in the current transaction,
+ * 3) this block has been writeback on disk in the current transactoin,
+ * 4) this block belongs to TREE_RELOC tree.
+ * 5) this block may be shared, and its generation is not transid
+ * (we need to ensure every parents has a proper node_ptr_gen)
*
* 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)) &&
- !root->force_cow)
- return 0;
- return 1;
+ if (root->force_cow)
+ return 1;
+ if (btrfs_header_generation(buf) < trans->transaction->transid)
+ return 1;
+ if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN))
+ return 1;
+ if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
+ btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC))
+ return 1;
+ if (btrfs_block_can_be_shared(root, buf) &&
+ must_update_generation(trans, root, buf))
+ return 1;
+
+ return 0;
}
/*
--
1.6.5.2
--
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