From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9978EC4CEC4 for ; Wed, 18 Sep 2019 06:32:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6735F218AE for ; Wed, 18 Sep 2019 06:32:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568788330; bh=PRWKNcqBpzKR0r42LB1UrY8958YYB9J4xHEDHt+uVTI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=K24PUcbYsspr5gIciH9S72TJ+DSTArNRjqaFj1qn8Pdp8hvV0xri/6u1G5WEE2SVT DAcFj9kGrbSKWe5XgbfCctaGOgImuRYjECZeUVT9eGK8TbDNPNIFqwnkZeGkP+TCWn t5K1dOf23+qQnZjN2lGVzbUDlbBVXjTfGUwM22P4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729370AbfIRGW1 (ORCPT ); Wed, 18 Sep 2019 02:22:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:42346 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbfIRGWZ (ORCPT ); Wed, 18 Sep 2019 02:22:25 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B9A8E21906; Wed, 18 Sep 2019 06:22:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568787744; bh=PRWKNcqBpzKR0r42LB1UrY8958YYB9J4xHEDHt+uVTI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SgEfY5q9Wzyr4uXfHAFlNn6EoDktjFoLWEhxoFAipIZhDnQVfz51QpFXb5k9EfxY/ 97ot3ukayeGElVrJMlVEN4olLvJQPKmT39HDbCdj30uZq/r+nN7E1D5nK/qlS7frsh YpGYBm6FBMFHEMhsvegU/09R5g2A5TzwPbJGrODc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , Filipe Manana , David Sterba Subject: [PATCH 4.19 18/50] Btrfs: fix assertion failure during fsync and use of stale transaction Date: Wed, 18 Sep 2019 08:19:01 +0200 Message-Id: <20190918061224.926360825@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190918061223.116178343@linuxfoundation.org> References: <20190918061223.116178343@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Filipe Manana commit 410f954cb1d1c79ae485dd83a175f21954fd87cd upstream. Sometimes when fsync'ing a file we need to log that other inodes exist and when we need to do that we acquire a reference on the inodes and then drop that reference using iput() after logging them. That generally is not a problem except if we end up doing the final iput() (dropping the last reference) on the inode and that inode has a link count of 0, which can happen in a very short time window if the logging path gets a reference on the inode while it's being unlinked. In that case we end up getting the eviction callback, btrfs_evict_inode(), invoked through the iput() call chain which needs to drop all of the inode's items from its subvolume btree, and in order to do that, it needs to join a transaction at the helper function evict_refill_and_join(). However because the task previously started a transaction at the fsync handler, btrfs_sync_file(), it has current->journal_info already pointing to a transaction handle and therefore evict_refill_and_join() will get that transaction handle from btrfs_join_transaction(). From this point on, two different problems can happen: 1) evict_refill_and_join() will often change the transaction handle's block reserve (->block_rsv) and set its ->bytes_reserved field to a value greater than 0. If evict_refill_and_join() never commits the transaction, the eviction handler ends up decreasing the reference count (->use_count) of the transaction handle through the call to btrfs_end_transaction(), and after that point we have a transaction handle with a NULL ->block_rsv (which is the value prior to the transaction join from evict_refill_and_join()) and a ->bytes_reserved value greater than 0. If after the eviction/iput completes the inode logging path hits an error or it decides that it must fallback to a transaction commit, the btrfs fsync handle, btrfs_sync_file(), gets a non-zero value from btrfs_log_dentry_safe(), and because of that non-zero value it tries to commit the transaction using a handle with a NULL ->block_rsv and a non-zero ->bytes_reserved value. This makes the transaction commit hit an assertion failure at btrfs_trans_release_metadata() because ->bytes_reserved is not zero but the ->block_rsv is NULL. The produced stack trace for that is like the following: [192922.917158] assertion failed: !trans->bytes_reserved, file: fs/btrfs/transaction.c, line: 816 [192922.917553] ------------[ cut here ]------------ [192922.917922] kernel BUG at fs/btrfs/ctree.h:3532! [192922.918310] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [192922.918666] CPU: 2 PID: 883 Comm: fsstress Tainted: G W 5.1.4-btrfs-next-47 #1 [192922.919035] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014 [192922.919801] RIP: 0010:assfail.constprop.25+0x18/0x1a [btrfs] (...) [192922.920925] RSP: 0018:ffffaebdc8a27da8 EFLAGS: 00010286 [192922.921315] RAX: 0000000000000051 RBX: ffff95c9c16a41c0 RCX: 0000000000000000 [192922.921692] RDX: 0000000000000000 RSI: ffff95cab6b16838 RDI: ffff95cab6b16838 [192922.922066] RBP: ffff95c9c16a41c0 R08: 0000000000000000 R09: 0000000000000000 [192922.922442] R10: ffffaebdc8a27e70 R11: 0000000000000000 R12: ffff95ca731a0980 [192922.922820] R13: 0000000000000000 R14: ffff95ca84c73338 R15: ffff95ca731a0ea8 [192922.923200] FS: 00007f337eda4e80(0000) GS:ffff95cab6b00000(0000) knlGS:0000000000000000 [192922.923579] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [192922.923948] CR2: 00007f337edad000 CR3: 00000001e00f6002 CR4: 00000000003606e0 [192922.924329] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [192922.924711] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [192922.925105] Call Trace: [192922.925505] btrfs_trans_release_metadata+0x10c/0x170 [btrfs] [192922.925911] btrfs_commit_transaction+0x3e/0xaf0 [btrfs] [192922.926324] btrfs_sync_file+0x44c/0x490 [btrfs] [192922.926731] do_fsync+0x38/0x60 [192922.927138] __x64_sys_fdatasync+0x13/0x20 [192922.927543] do_syscall_64+0x60/0x1c0 [192922.927939] entry_SYSCALL_64_after_hwframe+0x49/0xbe (...) [192922.934077] ---[ end trace f00808b12068168f ]--- 2) If evict_refill_and_join() decides to commit the transaction, it will be able to do it, since the nested transaction join only increments the transaction handle's ->use_count reference counter and it does not prevent the transaction from getting committed. This means that after eviction completes, the fsync logging path will be using a transaction handle that refers to an already committed transaction. What happens when using such a stale transaction can be unpredictable, we are at least having a use-after-free on the transaction handle itself, since the transaction commit will call kmem_cache_free() against the handle regardless of its ->use_count value, or we can end up silently losing all the updates to the log tree after that iput() in the logging path, or using a transaction handle that in the meanwhile was allocated to another task for a new transaction, etc, pretty much unpredictable what can happen. In order to fix both of them, instead of using iput() during logging, use btrfs_add_delayed_iput(), so that the logging path of fsync never drops the last reference on an inode, that step is offloaded to a safe context (usually the cleaner kthread). The assertion failure issue was sporadically triggered by the test case generic/475 from fstests, which loads the dm error target while fsstress is running, which lead to fsync failing while logging inodes with -EIO errors and then trying later to commit the transaction, triggering the assertion failure. CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/tree-log.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -5107,7 +5107,7 @@ again: BTRFS_I(other_inode), LOG_OTHER_INODE, 0, LLONG_MAX, ctx); - iput(other_inode); + btrfs_add_delayed_iput(other_inode); if (err) goto out_unlock; else @@ -5519,7 +5519,7 @@ process_leaf: } if (btrfs_inode_in_log(BTRFS_I(di_inode), trans->transid)) { - iput(di_inode); + btrfs_add_delayed_iput(di_inode); break; } @@ -5531,7 +5531,7 @@ process_leaf: if (!ret && btrfs_must_commit_transaction(trans, BTRFS_I(di_inode))) ret = 1; - iput(di_inode); + btrfs_add_delayed_iput(di_inode); if (ret) goto next_dir_inode; if (ctx->log_new_dentries) { @@ -5678,7 +5678,7 @@ static int btrfs_log_all_parents(struct if (!ret && ctx && ctx->log_new_dentries) ret = log_new_dir_dentries(trans, root, BTRFS_I(dir_inode), ctx); - iput(dir_inode); + btrfs_add_delayed_iput(dir_inode); if (ret) goto out; }