From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793214196; b=v3fDEhloQXoweE85UCNRaMLKFVX5MZHo2TAzcwYHbyjTygkQBJ6qO9DiSAPDB9S/c1sQ S6RsZheg3Z/4uJFWClilONjlZwyBDBoG8shSdPFO1shg8F8D4HbKRjaUGpQBc93ExppzH mZ7jRn3U1VK1ExodyRjH5HqazVAu74XbK4lv3weORUdhIOem6f6x78csSYwcVdOeAfwwU Ix37k08gOfGiGsFtRz4Mjms1qITyiJwOpawyMhxCRyAtZmEhO4qyG+zMXIOFqG/OZkSlH eP4+s5vEnqAwt0ekC2Og+Mxj0wOuaLSYvRrCah7aVTw8AnrQ+BOnj14IwAmzn3mLGaA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793214196; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=OgasbLjIAbVaj2RSxxUsZNX3iQFbkU0p6mpJJTXcP0A=; b=IEuK7Z4BNIKF16OL/MKoU/+F7DtyqoNpyXXQHRJ4rXlgOpVAUYHqbv2GijCesmpY6yJC 1br+6M4DdNCIN9oOuuTl4eRn74ZPmGt1EF4Lvzg8k3DIXR48I/CCcTyBzAnd9nIKHeriH Pl6xZscwWSJ75abLW6TJM6DsHopS8Eto9tUW2aTqYR4IzNFRWiTtjwbiS9/7DQ3NiVOxZ wXl/PQDlc8qal0SJ/eEAmNh9kS7Kv6sD1JwpWFCvmBo+ASZgi2d7bLB7icsz2GKOikPYZ u8voO/MbaTUTumnHgvh0POM8xVm1muFvlC95lks3HPjC7CRSyLDC/P0OULfAifEm4sQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=FUOez5m4; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC53460A6F6C; Wed, 28 Oct 2026 19:03:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=FUOez5m4 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 190461F013DA; Wed, 28 Oct 2026 19:03:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793214195; bh=OgasbLjIAbVaj2RSxxUsZNX3iQFbkU0p6mpJJTXcP0A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=FUOez5m4Aj82fIKtmEUFuzJ/myIB+D0ZQ60ZnhM/6KJ7+qhW4L141Ve6rEZO6mafW QTa74T0tEEYumN0iJAHQlMbEQPQUtdcBBPSNA4D4xOgbr9tPDM/Q3GfJKFkuW2/D5D UqkEIDyHqhi2tNNuCF2IJuGyqSKGderXjyHQ9mWc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Qu Wenruo , Filipe Manana , Boris Burkov , David Sterba , Sasha Levin Subject: [PATCH 6.1 0774/1887] btrfs: harden block_group::bg_list against list_del() races Date: Wed, 28 Oct 2026 17:47:50 +0100 Message-ID: <20261028170517.052579882@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170459.200466217@linuxfoundation.org> References: <20261028170459.200466217@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ 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 a09ac37f7cf48..3ecb3d0018a18 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2834,7 +2834,15 @@ 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 af7b5aae842a8..6b9a41c939d28 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -148,7 +148,13 @@ 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); } @@ -2104,7 +2110,13 @@ 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_delayed_refs_rsv_release(fs_info, 1); + /* + * 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); } } -- 2.53.0