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Commit d43317dc authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: fix race during transaction joins 



While we're allocating ram for a new transaction, we drop our spinlock.
When we get the lock back, we do check to see if a transaction started
while we slept, but we don't check to make sure it isn't blocked
because a commit has already started.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 56d2a48f

fs/btrfs/transaction.c

+8 −5
Original line number Diff line number Diff line
@@ -55,6 +55,7 @@ static noinline int join_transaction(struct btrfs_root *root, int nofail) 
	struct btrfs_transaction *cur_trans;



	spin_lock(&root->fs_info->trans_lock);

loop:

	if (root->fs_info->trans_no_join) {

		if (!nofail) {

			spin_unlock(&root->fs_info->trans_lock);
@@ -75,16 +76,18 @@ static noinline int join_transaction(struct btrfs_root *root, int nofail) 
	cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);

	if (!cur_trans)

		return -ENOMEM;



	spin_lock(&root->fs_info->trans_lock);

	if (root->fs_info->running_transaction) {

		/*

		 * someone started a transaction after we unlocked.  Make sure

		 * to redo the trans_no_join checks above

		 */

		kmem_cache_free(btrfs_transaction_cachep, cur_trans);

		cur_trans = root->fs_info->running_transaction;

		atomic_inc(&cur_trans->use_count);

		atomic_inc(&cur_trans->num_writers);

		cur_trans->num_joined++;

		spin_unlock(&root->fs_info->trans_lock);

		return 0;

		goto loop;

	}



	atomic_set(&cur_trans->num_writers, 1);

	cur_trans->num_joined = 0;

	init_waitqueue_head(&cur_trans->writer_wait);