Btrfs: fix race with freeze and free space inodes (98114659) · Commits · 戴 / test

So we start our freeze, somebody comes in and does an fsync() on a file where we have to commit a transaction for whatever reason, and we will deadlock because the freeze is waiting on FS_FREEZE people to stop writing to the file system, but the transaction is waiting for its free space inodes to be written out, which are in turn waiting on sb_start_intwrite while trying to write the file extents. To fix this we'll just skip the sb_start_intwrite() if we TRANS_JOIN_NOLOCK since we're being waited on by a transaction commit so we're safe wrt to freeze and this will keep us from deadlocking. Thanks, Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/transaction.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -342,7 +342,15 @@ again:
		if (!h)
		return ERR_PTR(-ENOMEM);

		if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
		/*
		* If we are JOIN_NOLOCK we're already committing a transaction and
		* waiting on this guy, so we don't need to do the sb_start_intwrite
		* because we're already holding a ref. We need this because we could
		* have raced in and did an fsync() on a file which can kick a commit
		* and then we deadlock with somebody doing a freeze.
		*/
		if (type != TRANS_JOIN_NOLOCK &&
		!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
		if (type == TRANS_JOIN_FREEZE)
		return ERR_PTR(-EPERM);
		sb_start_intwrite(root->fs_info->sb);
		@@ -601,6 +609,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
		}
		}

		if (lock)
		sb_end_intwrite(root->fs_info->sb);

		WARN_ON(cur_trans != info->running_transaction);

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