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 EDDB3255E23; Thu, 17 Apr 2025 18:01:03 +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=1744912864; cv=none; b=qvmoL6449vuLV9YFkX5lY65OJatiGdTy7xE7cGZXmieYtGIM/U8m2XqPkyl+YhAkIgUmrqGoEP0d4/rUeYfS7pq0zu9m72FwTZhrerSehh9mfZZt6Dm2k9k8hXNuIABxB3HUjdjY/MvLUHoVMi+B3j19/P1SdlYbIxl1EWsEEng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744912864; c=relaxed/simple; bh=d83tcuQ4GKJhpo6h6VJM5mIWnRYmzVcPk6qdGG+l1fw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GVZ66HrCxFEl5hKFg5V0Kc4YiG0s6JgQDm+DfAVKdIcD7+z0IG5Wgl4D4WXRJAKFOjYQeMM7QsQv2O+zR+EBajENFRmH1cRJgPWCnEEoJKV4iCW1hnzmxTcuLk5r0SX/ywdt0d3Zi0T+0XpO44I7a8dt3QLgUWe2rHIB/7nc9SI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=d5WwGi6A; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="d5WwGi6A" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A9EBC4CEE4; Thu, 17 Apr 2025 18:01:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1744912863; bh=d83tcuQ4GKJhpo6h6VJM5mIWnRYmzVcPk6qdGG+l1fw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=d5WwGi6AUV6A0pIt6o+NEvL29Ibb+joeBnamWE3jFnOC+k7p38Ji3Q/y/Ae9jRXX0 FtTmyqJeQWo6uIyt3Qh+iw+QU5TnMYBK8guS4oFsSK8nMtEhfssUDPDBzdcbIfWddI yhNmOIv6v6k/XiI15jvWwLTliQEBTxEfIfZ9tjlc= 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 6.14 132/449] btrfs: harden block_group::bg_list against list_del() races Date: Thu, 17 Apr 2025 19:47:00 +0200 Message-ID: <20250417175123.279828147@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250417175117.964400335@linuxfoundation.org> References: <20250417175117.964400335@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.14-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 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