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=-9.8 required=3.0 tests=BAYES_00,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=unavailable 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 A290CC433DF for ; Thu, 20 Aug 2020 09:26:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F69922D07 for ; Thu, 20 Aug 2020 09:26:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597915578; bh=yftGnr7TyooLqUgV7TUEcQ9nkwaYA4xThnSHYjZ/N6k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TpMcbVyPdy+Q1eg0SSrmA6DN8STjh6aSrY98fPRaxTEYiUzk3VsDD4VmH8KDrUMYx 06XC33xYYbWhDxxT1mVe1k83z5cFHVTTEdvIEU2/senzKPoEbjPLtuvZbzCtLUbH+K lU+j6Xqse/boTB5fmyKGKlPPeB/lWD+2/twl3eQc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727851AbgHTJ0I (ORCPT ); Thu, 20 Aug 2020 05:26:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:33272 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726795AbgHTJZB (ORCPT ); Thu, 20 Aug 2020 05:25:01 -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 212F322CB1; Thu, 20 Aug 2020 09:24:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597915500; bh=yftGnr7TyooLqUgV7TUEcQ9nkwaYA4xThnSHYjZ/N6k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=grWl6KE5tcNErUGDrk0OKbeisU+xUyqlOD+N/Sb1c3Hp0UqsATh76TEmAU4k2S0Of +ds9dGGgwmJvjrMRPesDHuEf+VYfGtSXTcuwO8AFSuYuNjO/pEjJoCW5CxfI6OBwGP 2S8Ggf9/cTgD93tCCYEAJ9BI/f+9CuQVFBj/n1mM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , Qu Wenruo , David Sterba Subject: [PATCH 5.8 028/232] btrfs: avoid possible signal interruption of btrfs_drop_snapshot() on relocation tree Date: Thu, 20 Aug 2020 11:17:59 +0200 Message-Id: <20200820091614.116316607@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200820091612.692383444@linuxfoundation.org> References: <20200820091612.692383444@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: Qu Wenruo commit f3e3d9cc35252a70a2fd698762c9687718268ec6 upstream. [BUG] There is a bug report about bad signal timing could lead to read-only fs during balance: BTRFS info (device xvdb): balance: start -d -m -s BTRFS info (device xvdb): relocating block group 73001861120 flags metadata BTRFS info (device xvdb): found 12236 extents, stage: move data extents BTRFS info (device xvdb): relocating block group 71928119296 flags data BTRFS info (device xvdb): found 3 extents, stage: move data extents BTRFS info (device xvdb): found 3 extents, stage: update data pointers BTRFS info (device xvdb): relocating block group 60922265600 flags metadata BTRFS: error (device xvdb) in btrfs_drop_snapshot:5505: errno=-4 unknown BTRFS info (device xvdb): forced readonly BTRFS info (device xvdb): balance: ended with status: -4 [CAUSE] The direct cause is the -EINTR from the following call chain when a fatal signal is pending: relocate_block_group() |- clean_dirty_subvols() |- btrfs_drop_snapshot() |- btrfs_start_transaction() |- btrfs_delayed_refs_rsv_refill() |- btrfs_reserve_metadata_bytes() |- __reserve_metadata_bytes() |- wait_reserve_ticket() |- prepare_to_wait_event(); |- ticket->error = -EINTR; Normally this behavior is fine for most btrfs_start_transaction() callers, as they need to catch any other error, same for the signal, and exit ASAP. However for balance, especially for the clean_dirty_subvols() case, we're already doing cleanup works, getting -EINTR from btrfs_drop_snapshot() could cause a lot of unexpected problems. >>From the mentioned forced read-only report, to later balance error due to half dropped reloc trees. [FIX] Fix this problem by using btrfs_join_transaction() if btrfs_drop_snapshot() is called from relocation context. Since btrfs_join_transaction() won't get interrupted by signal, we can continue the cleanup. CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Josef Bacik Signed-off-by: Qu Wenruo Reviewed-by: David Sterba 3 Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/extent-tree.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -5298,7 +5298,14 @@ int btrfs_drop_snapshot(struct btrfs_roo goto out; } - trans = btrfs_start_transaction(tree_root, 0); + /* + * Use join to avoid potential EINTR from transaction start. See + * wait_reserve_ticket and the whole reservation callchain. + */ + if (for_reloc) + trans = btrfs_join_transaction(tree_root); + else + trans = btrfs_start_transaction(tree_root, 0); if (IS_ERR(trans)) { err = PTR_ERR(trans); goto out_free;