Commit f1ebcc74 authored by Liu Bo's avatar Liu Bo Committed by Chris Mason
Browse files

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: default avatarLiu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 8965593e

fs/btrfs/ctree.c

+16 −1
Original line number Diff line number Diff line
@@ -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;

}

fs/btrfs/ctree.h

+2 −0
Original line number Diff line number Diff line
@@ -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 {

fs/btrfs/transaction.c

+8 −0
Original line number Diff line number Diff line
@@ -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;

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