From patchwork Wed Apr 17 10:30:30 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Filipe Manana X-Patchwork-Id: 10905137 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E024217E0 for ; Wed, 17 Apr 2019 10:30:56 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C7485288C3 for ; Wed, 17 Apr 2019 10:30:56 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B8BC728A47; Wed, 17 Apr 2019 10:30:56 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A2614288C3 for ; Wed, 17 Apr 2019 10:30:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728373AbfDQKag (ORCPT ); Wed, 17 Apr 2019 06:30:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:32970 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726695AbfDQKag (ORCPT ); Wed, 17 Apr 2019 06:30:36 -0400 Received: from localhost.localdomain (bl8-197-74.dsl.telepac.pt [85.241.197.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CC4D521773; Wed, 17 Apr 2019 10:30:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555497034; bh=d5zRrsaK9PC/9ViGMEw2Khfe1//gCYswslCpZrx/sSY=; h=From:To:Cc:Subject:Date:From; b=nU7bUNOCpJIxZtm7o5Pgd9TZTAj6IdN33W5JJPNoiU+7/o8Mc3lDp5rkxv2oRNX/G b3d6X458Iu6XErbURvwILnlB5rSk6KsDsPOgfdsowdFmwJMTjXZnWFEvWgyl98JuHt RFFBrwSX2onOIxJyhAyZXMdvKPJKk445m9NiWTlw= From: fdmanana@kernel.org To: linux-btrfs@vger.kernel.org Cc: ce3g8jdj@umail.furryterror.org Subject: [PATCH] Btrfs: do not start a transaction at iterate_extent_inodes() Date: Wed, 17 Apr 2019 11:30:30 +0100 Message-Id: <20190417103030.24883-1-fdmanana@kernel.org> X-Mailer: git-send-email 2.11.0 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Filipe Manana When finding out which inodes have references on a particular extent, done by backref.c:iterate_extent_inodes(), from the BTRFS_IOC_LOGICAL_INO (both v1 and v2) ioctl and from scrub we use the transaction join api to grab a reference on the currently running transaction, since in order to give accurate results we need to inspect the delayed references of the currently running transaction. However, if there is currently no running transaction, the join operation will create a new transaction. This is inneficient as the transaction will eventually be committed, doing unnecessary IO and introducing a potential point of failure that will lead to a transaction abort due to -ENOSPC, as recently reported [1]. That's because the join, creates the transaction but does not reserves any space, so when attempting to update the root item of the root passed to btrfs_join_transaction(), during the transaction commit, we can end up failling with -ENOSPC. Users of a join operation are supposed to actually do some filesystem changes and reserve space by some means, which is not the case of iterate_extent_inodes(), it is a read-only operation for all contextes from which it is called. The reported [1] -ENOSPC failure stack trace is the following: heisenberg kernel: ------------[ cut here ]------------ heisenberg kernel: BTRFS: Transaction aborted (error -28) heisenberg kernel: WARNING: CPU: 0 PID: 7137 at fs/btrfs/root-tree.c:136 btrfs_update_root+0x22b/0x320 [btrfs] (...) heisenberg kernel: CPU: 0 PID: 7137 Comm: btrfs-transacti Not tainted 4.19.0-4-amd64 #1 Debian 4.19.28-2 heisenberg kernel: Hardware name: FUJITSU LIFEBOOK U757/FJNB2A5, BIOS Version 1.21 03/19/2018 heisenberg kernel: RIP: 0010:btrfs_update_root+0x22b/0x320 [btrfs] (...) heisenberg kernel: RSP: 0018:ffffb5448828bd40 EFLAGS: 00010286 heisenberg kernel: RAX: 0000000000000000 RBX: ffff8ed56bccef50 RCX: 0000000000000006 heisenberg kernel: RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff8ed6bda166a0 heisenberg kernel: RBP: 00000000ffffffe4 R08: 00000000000003df R09: 0000000000000007 heisenberg kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff8ed63396a078 heisenberg kernel: R13: ffff8ed092d7c800 R14: ffff8ed64f5db028 R15: ffff8ed6bd03d068 heisenberg kernel: FS: 0000000000000000(0000) GS:ffff8ed6bda00000(0000) knlGS:0000000000000000 heisenberg kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 heisenberg kernel: CR2: 00007f46f75f8000 CR3: 0000000310a0a002 CR4: 00000000003606f0 heisenberg kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 heisenberg kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 heisenberg kernel: Call Trace: heisenberg kernel: commit_fs_roots+0x166/0x1d0 [btrfs] heisenberg kernel: ? _cond_resched+0x15/0x30 heisenberg kernel: ? btrfs_run_delayed_refs+0xac/0x180 [btrfs] heisenberg kernel: btrfs_commit_transaction+0x2bd/0x870 [btrfs] heisenberg kernel: ? start_transaction+0x9d/0x3f0 [btrfs] heisenberg kernel: transaction_kthread+0x147/0x180 [btrfs] heisenberg kernel: ? btrfs_cleanup_transaction+0x530/0x530 [btrfs] heisenberg kernel: kthread+0x112/0x130 heisenberg kernel: ? kthread_bind+0x30/0x30 heisenberg kernel: ret_from_fork+0x35/0x40 heisenberg kernel: ---[ end trace 05de912e30e012d9 ]--- So fix that by using the attach API, which does not create a transaction when there is currently no running transaction. [1] https://lore.kernel.org/linux-btrfs/b2a668d7124f1d3e410367f587926f622b3f03a4.camel@scientia.net/ Reported-by: Zygo Blaxell Signed-off-by: Filipe Manana --- fs/btrfs/backref.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index 6d616737f349..fd4d968f1b41 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -1916,13 +1916,19 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info, extent_item_objectid); if (!search_commit_root) { - trans = btrfs_join_transaction(fs_info->extent_root); - if (IS_ERR(trans)) - return PTR_ERR(trans); + trans = btrfs_attach_transaction(fs_info->extent_root); + if (IS_ERR(trans)) { + if (PTR_ERR(trans) != -ENOENT && + PTR_ERR(trans) != -EROFS) + return PTR_ERR(trans); + trans = NULL; + } + } + + if (trans) btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem); - } else { + else down_read(&fs_info->commit_root_sem); - } ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid, tree_mod_seq_elem.seq, &refs, @@ -1955,7 +1961,7 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info, free_leaf_list(refs); out: - if (!search_commit_root) { + if (trans) { btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem); btrfs_end_transaction(trans); } else {