From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 822D625C6EE; Thu, 3 Apr 2025 19:03:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743707024; cv=none; b=DJ3t1x+V9qNLzBUCvhmwX8rE9HNGshkRIe/lQcuUyrqANr326SmJx0nQQDlRZxRkgTtJ7Hd555a+xLIBe4IHuOG5OODI2mNA9i68IKgm8mjU9LO0nvr0+8zYs9KkPkmoEyHxI6eytR3+qCIZE7w36nYWrG06kVBWhXu3cAI08dU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743707024; c=relaxed/simple; bh=ocUmumNNqTn8lwXlmZIoT+GwMG8uU3C5LnKpYpZ+rKc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=IBXOTpP0xeff3QYxuyoQr6u0INsMMb7MlKXRODz8fgWvDV+3eSBRPbrhIghJbeBhwmyS2C3FJI4r7hH1JYo7DM82lpiu7XmJcCc8n8nHUm1qPJ71rIf2Wua4FcONhB/Zdrd1pg+lNgxYDRbyEF4Fr4ajbRkCFOmQQL/fXT78aVY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MaiGOzT6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MaiGOzT6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E7F49C4CEE9; Thu, 3 Apr 2025 19:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743707024; bh=ocUmumNNqTn8lwXlmZIoT+GwMG8uU3C5LnKpYpZ+rKc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MaiGOzT6YEDeOAHSFt5JFavP98pkaVYGuDEEC0uxMYLlc5/Qvv6wE7defhXXhWIuj H9PIgQrVCLYa4oF/2gz8OFH3LmvsZaP0rTrds2gmgA/3w9ffIi/OuSCmcf6oMQ8wtf AXP7rEGcADiJKv54hKh/UElK52Sx6BNNV2Vhe3xIAV1j4zKS0ASVraTzTXOQGReG/J nhQ4c/nXaJOxKERWt6VFhwTk2DMdflBbpmLa9q/JZSggQ+KHqEL6H1dej3XHSh9smI 8spUUszMzwsTX2+qS31+NbWzsISPPJp0ipc1huI9LxISJTEuEO+G4XfuOTbx5A7hfZ EVzq6QXYnIypw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Boris Burkov , Qu Wenruo , Filipe Manana , David Sterba , Sasha Levin , clm@fb.com, josef@toxicpanda.com, linux-btrfs@vger.kernel.org Subject: [PATCH AUTOSEL 6.14 41/54] btrfs: harden block_group::bg_list against list_del() races Date: Thu, 3 Apr 2025 15:01:56 -0400 Message-Id: <20250403190209.2675485-41-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250403190209.2675485-1-sashal@kernel.org> References: <20250403190209.2675485-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.14 Content-Transfer-Encoding: 8bit From: Boris Burkov [ Upstream commit 7511e29cf1355b2c47d0effb39e463119913e2f6 ] As far as I can tell, these calls of list_del_init() on bg_list cannot run concurrently with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(), as they are in transaction error paths and situations where the block group is readonly. However, if there is any chance at all of racing with mark_bg_unused(), or a different future user of bg_list, better to be safe than sorry. Otherwise we risk the following interleaving (bg_list refcount in parens) T1 (some random op) T2 (btrfs_mark_bg_unused) !list_empty(&bg->bg_list); (1) list_del_init(&bg->bg_list); (1) list_move_tail (1) btrfs_put_block_group (0) btrfs_delete_unused_bgs bg = list_first_entry list_del_init(&bg->bg_list); btrfs_put_block_group(bg); (-1) Ultimately, this results in a broken ref count that hits zero one deref early and the real final deref underflows the refcount, resulting in a WARNING. Reviewed-by: Qu Wenruo Reviewed-by: Filipe Manana Signed-off-by: Boris Burkov Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/extent-tree.c | 8 ++++++++ fs/btrfs/transaction.c | 12 ++++++++++++ 2 files changed, 20 insertions(+) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 3014a1a23efdb..6d615711f0400 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2874,7 +2874,15 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans) block_group->length, &trimmed); + /* + * Not strictly necessary to lock, as the block_group should be + * read-only from btrfs_delete_unused_bgs(). + */ + ASSERT(block_group->ro); + spin_lock(&fs_info->unused_bgs_lock); list_del_init(&block_group->bg_list); + spin_unlock(&fs_info->unused_bgs_lock); + btrfs_unfreeze_block_group(block_group); btrfs_put_block_group(block_group); diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index aca83a98b75a2..c0e9d4bbe380d 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -160,7 +160,13 @@ void btrfs_put_transaction(struct btrfs_transaction *transaction) cache = list_first_entry(&transaction->deleted_bgs, struct btrfs_block_group, bg_list); + /* + * Not strictly necessary to lock, as no other task will be using a + * block_group on the deleted_bgs list during a transaction abort. + */ + spin_lock(&transaction->fs_info->unused_bgs_lock); list_del_init(&cache->bg_list); + spin_unlock(&transaction->fs_info->unused_bgs_lock); btrfs_unfreeze_block_group(cache); btrfs_put_block_group(cache); } @@ -2096,7 +2102,13 @@ static void btrfs_cleanup_pending_block_groups(struct btrfs_trans_handle *trans) list_for_each_entry_safe(block_group, tmp, &trans->new_bgs, bg_list) { btrfs_dec_delayed_refs_rsv_bg_inserts(fs_info); + /* + * Not strictly necessary to lock, as no other task will be using a + * block_group on the new_bgs list during a transaction abort. + */ + spin_lock(&fs_info->unused_bgs_lock); list_del_init(&block_group->bg_list); + spin_unlock(&fs_info->unused_bgs_lock); } } -- 2.39.5