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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,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 C46EBC2BB85 for ; Fri, 10 Apr 2020 03:52:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9D70120936 for ; Fri, 10 Apr 2020 03:52:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586490727; bh=ZYbwXhYowYbtrutQRkQ/iDxc67+bXJ9149QcEAIzph8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=gkdiWRN2hcC67okyzdvhbfKIXVqdF5aTyjpmUanWIPwbdSBarj0IX4az3gYNtOV5F aZZ3N9RMDqI38aOp8sH1INKR74igO3+3Cn0TJNvxLuX1BqplBNTlBvKowE9sUmUl5T 1J9tt3rf21xFPVW+ToeLsWyvwhrYg2tAHq5lBVrY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728353AbgDJDwG (ORCPT ); Thu, 9 Apr 2020 23:52:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:36508 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729163AbgDJDvU (ORCPT ); Thu, 9 Apr 2020 23:51:20 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (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 56FAA2173E; Fri, 10 Apr 2020 03:51:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586490680; bh=ZYbwXhYowYbtrutQRkQ/iDxc67+bXJ9149QcEAIzph8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c+KP46RPIAOg4ZfQxAV/lMjT9gkgStufsaCfW/IQh5yXFHdgpRSY1Mvbntw3q3yUZ AbBgseJqByQoe/pJFdB3aQLgF5Y4SP0rrmgcQ0F3pAUux9B6qi84B9TJ83veACpUZ6 aYc2hzgMJcF1oNlmj8m6wLWj81p31MqYQQZV+RvQ= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Josef Bacik , Qu Wenruo , David Sterba , Sasha Levin , linux-btrfs@vger.kernel.org Subject: [PATCH AUTOSEL 4.9 8/9] btrfs: remove a BUG_ON() from merge_reloc_roots() Date: Thu, 9 Apr 2020 23:51:09 -0400 Message-Id: <20200410035111.9938-8-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200410035111.9938-1-sashal@kernel.org> References: <20200410035111.9938-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Josef Bacik [ Upstream commit 7b7b74315b24dc064bc1c683659061c3d48f8668 ] This was pretty subtle, we default to reloc roots having 0 root refs, so if we crash in the middle of the relocation they can just be deleted. If we successfully complete the relocation operations we'll set our root refs to 1 in prepare_to_merge() and then go on to merge_reloc_roots(). At prepare_to_merge() time if any of the reloc roots have a 0 reference still, we will remove that reloc root from our reloc root rb tree, and then clean it up later. However this only happens if we successfully start a transaction. If we've aborted previously we will skip this step completely, and only have reloc roots with a reference count of 0, but were never properly removed from the reloc control's rb tree. This isn't a problem per-se, our references are held by the list the reloc roots are on, and by the original root the reloc root belongs to. If we end up in this situation all the reloc roots will be added to the dirty_reloc_list, and then properly dropped at that point. The reloc control will be free'd and the rb tree is no longer used. There were two options when fixing this, one was to remove the BUG_ON(), the other was to make prepare_to_merge() handle the case where we couldn't start a trans handle. IMO this is the cleaner solution. I started with handling the error in prepare_to_merge(), but it turned out super ugly. And in the end this BUG_ON() simply doesn't matter, the cleanup was happening properly, we were just panicing because this BUG_ON() only matters in the success case. So I've opted to just remove it and add a comment where it was. Reviewed-by: Qu Wenruo Signed-off-by: Josef Bacik Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/relocation.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index b106d365257d3..97bc85ca508c2 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -2457,7 +2457,21 @@ void merge_reloc_roots(struct reloc_control *rc) free_reloc_roots(&reloc_roots); } - BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root)); + /* + * We used to have + * + * BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root)); + * + * here, but it's wrong. If we fail to start the transaction in + * prepare_to_merge() we will have only 0 ref reloc roots, none of which + * have actually been removed from the reloc_root_tree rb tree. This is + * fine because we're bailing here, and we hold a reference on the root + * for the list that holds it, so these roots will be cleaned up when we + * do the reloc_dirty_list afterwards. Meanwhile the root->reloc_root + * will be cleaned up on unmount. + * + * The remaining nodes will be cleaned up by free_reloc_control. + */ } static void free_block_list(struct rb_root *blocks) -- 2.20.1