From patchwork Tue May 2 13:38:46 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Michal_Koutn=C3=BD?= X-Patchwork-Id: 13228944 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED488C7EE21 for ; Tue, 2 May 2023 13:41:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234493AbjEBNlH (ORCPT ); Tue, 2 May 2023 09:41:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234322AbjEBNkm (ORCPT ); Tue, 2 May 2023 09:40:42 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56B70728F; Tue, 2 May 2023 06:39:59 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 165141FD64; Tue, 2 May 2023 13:38:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1683034730; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=I/j4j9VxXGy/bDa3ZnK1aishpl8LLc1RBAztW/6LzNg=; b=TcCfrFzTb2GRwJYnmkZtx/AUQ6ImGap2e8r4FxC9peMvwWganei9xc2rzw0XO7CkKJvoqD Kb7qic6qmYoUyjZu9jtT+UfyJjpew6bT/ifb+NBAP2VrlT1UNFXqAonzY3WLwYc7RUwYE4 tGeCU80e/++C4sgH6PfoViUwgJkFhnU= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id D26C3134FB; Tue, 2 May 2023 13:38:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id CFqdMmkSUWTOYQAAMHmgww (envelope-from ); Tue, 02 May 2023 13:38:49 +0000 From: =?utf-8?q?Michal_Koutn=C3=BD?= To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Cc: Alexander Viro , Christian Brauner , Tejun Heo , Zefan Li , Johannes Weiner , Dave Chinner , Rik van Riel , Jiri Wiesner Subject: [RFC PATCH 2/3] cgroup: Rely on namespace_sem in current_cgns_cgroup_from_root explicitly Date: Tue, 2 May 2023 15:38:46 +0200 Message-Id: <20230502133847.14570-3-mkoutny@suse.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230502133847.14570-1-mkoutny@suse.com> References: <20230502133847.14570-1-mkoutny@suse.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The function current_cgns_cgroup_from_root() expects a stable cgroup_root, which is currently ensured with RCU read side paired with cgroup_destroy_root() called after RCU period. The particular current_cgns_cgroup_from_root() is called from VFS code and cgroup_root stability can be also ensured by namespace_sem. Mark it explicitly as a preparation for further rework. Signed-off-by: Michal Koutný --- fs/namespace.c | 5 ++++- include/linux/mount.h | 4 ++++ kernel/cgroup/cgroup.c | 7 +++---- 3 files changed, 11 insertions(+), 5 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 54847db5b819..0d2333832064 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -71,7 +71,10 @@ static DEFINE_IDA(mnt_group_ida); static struct hlist_head *mount_hashtable __read_mostly; static struct hlist_head *mountpoint_hashtable __read_mostly; static struct kmem_cache *mnt_cache __read_mostly; -static DECLARE_RWSEM(namespace_sem); +DECLARE_RWSEM(namespace_sem); +#ifdef CONFIG_LOCKDEP +EXPORT_SYMBOL_GPL(namespace_sem); +#endif static HLIST_HEAD(unmounted); /* protected by namespace_sem */ static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */ diff --git a/include/linux/mount.h b/include/linux/mount.h index 1ea326c368f7..6277435f6748 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -80,6 +80,10 @@ static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt) return smp_load_acquire(&mnt->mnt_idmap); } +#ifdef CONFIG_LOCKDEP +extern struct rw_semaphore namespace_sem; +#endif + extern int mnt_want_write(struct vfsmount *mnt); extern int mnt_want_write_file(struct file *file); extern void mnt_drop_write(struct vfsmount *mnt); diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 55e5f0110e3b..32d693a797b9 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1440,13 +1440,12 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) lockdep_assert_held(&css_set_lock); - rcu_read_lock(); + /* namespace_sem ensures `root` stability on unmount */ + lockdep_assert(lockdep_is_held_type(&namespace_sem, -1)); cset = current->nsproxy->cgroup_ns->root_cset; res = __cset_cgroup_from_root(cset, root); - rcu_read_unlock(); - return res; } @@ -1454,7 +1453,7 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) * Look up cgroup associated with current task's cgroup namespace on the default * hierarchy. * - * Unlike current_cgns_cgroup_from_root(), this doesn't need locks: + * Relaxed locking requirements: * - Internal rcu_read_lock is unnecessary because we don't dereference any rcu * pointers. * - css_set_lock is not needed because we just read cset->dfl_cgrp.