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 B45CC1AE845; Thu, 15 Aug 2024 14:09:38 +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=1723730978; cv=none; b=osZTVp54sbjQbaxM+LWPB2iNVG+1QNNqbspMfWreFuwZBMHOuwbHoktX4ESSfznh/ViNTncmH2RrpiaEus2R2B8oQ+1T1fIUZ0LYPyslPxuCVxlqA2MX5cZKtrRNhjKm0AuaQHu0zhy3JVWtezNqmjq5TF2MaLQqEWpqhd/DAA4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723730978; c=relaxed/simple; bh=6b7MX9ByWcQGLh3QsIPmxUOsMLP2f5gDqznqnDN5NkU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=qsgmCE4uvbSzUDqVvtgc6iSjBU/VQsd/zPC9ozmXPrk1YLEsNYfbaejPpevYBa6908OK4pFZjz5J7W0jM4Jv7jB1Po5InbEKLcSS5ef0XkCK4aYyjlEdMk941cwA5VDkIyhkDgp1ByF4Wh04OjfERXT8R9OftlcSkvo+V0I900o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=n/xBbzDT; 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="n/xBbzDT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2E5F6C32786; Thu, 15 Aug 2024 14:09:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1723730978; bh=6b7MX9ByWcQGLh3QsIPmxUOsMLP2f5gDqznqnDN5NkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n/xBbzDTqAbejy6lFXVMUU9HbwW89v/5lQ2XnYl15iensRvqAPl1si6DcXOYAbN0k Y+GsFDuNhe+fI7r8lalukbAYMZ3T/fNVX45PgIdM/qV3jmxiiCyvL0wUZQpC9X9Kt1 OIZtFx992bfywUaL4+epNqJQdIZnU18+qGhpdAdQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org, =?UTF-8?q?Michal=20Koutn=C3=BD?= Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yafang Shao , Tejun Heo Subject: [PATCH 6.6 21/67] cgroup: Make operations on the cgroup root_list RCU safe Date: Thu, 15 Aug 2024 15:25:35 +0200 Message-ID: <20240815131839.149850850@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240815131838.311442229@linuxfoundation.org> References: <20240815131838.311442229@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yafang Shao commit d23b5c577715892c87533b13923306acc6243f93 upstream. At present, when we perform operations on the cgroup root_list, we must hold the cgroup_mutex, which is a relatively heavyweight lock. In reality, we can make operations on this list RCU-safe, eliminating the need to hold the cgroup_mutex during traversal. Modifications to the list only occur in the cgroup root setup and destroy paths, which should be infrequent in a production environment. In contrast, traversal may occur frequently. Therefore, making it RCU-safe would be beneficial. Signed-off-by: Yafang Shao Signed-off-by: Tejun Heo To: Michal Koutný Signed-off-by: Greg Kroah-Hartman --- include/linux/cgroup-defs.h | 1 + kernel/cgroup/cgroup-internal.h | 3 ++- kernel/cgroup/cgroup.c | 23 ++++++++++++++++------- 3 files changed, 19 insertions(+), 8 deletions(-) --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -558,6 +558,7 @@ struct cgroup_root { /* A list running through the active hierarchies */ struct list_head root_list; + struct rcu_head rcu; /* Hierarchy-specific flags */ unsigned int flags; --- a/kernel/cgroup/cgroup-internal.h +++ b/kernel/cgroup/cgroup-internal.h @@ -170,7 +170,8 @@ extern struct list_head cgroup_roots; /* iterate across the hierarchies */ #define for_each_root(root) \ - list_for_each_entry((root), &cgroup_roots, root_list) + list_for_each_entry_rcu((root), &cgroup_roots, root_list, \ + lockdep_is_held(&cgroup_mutex)) /** * for_each_subsys - iterate all enabled cgroup subsystems --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1313,7 +1313,7 @@ static void cgroup_exit_root_id(struct c void cgroup_free_root(struct cgroup_root *root) { - kfree(root); + kfree_rcu(root, rcu); } static void cgroup_destroy_root(struct cgroup_root *root) @@ -1346,7 +1346,7 @@ static void cgroup_destroy_root(struct c spin_unlock_irq(&css_set_lock); if (!list_empty(&root->root_list)) { - list_del(&root->root_list); + list_del_rcu(&root->root_list); cgroup_root_count--; } @@ -1386,7 +1386,15 @@ static inline struct cgroup *__cset_cgro } } - BUG_ON(!res_cgroup); + /* + * If cgroup_mutex is not held, the cgrp_cset_link will be freed + * before we remove the cgroup root from the root_list. Consequently, + * when accessing a cgroup root, the cset_link may have already been + * freed, resulting in a NULL res_cgroup. However, by holding the + * cgroup_mutex, we ensure that res_cgroup can't be NULL. + * If we don't hold cgroup_mutex in the caller, we must do the NULL + * check. + */ return res_cgroup; } @@ -1445,7 +1453,6 @@ static struct cgroup *current_cgns_cgrou static struct cgroup *cset_cgroup_from_root(struct css_set *cset, struct cgroup_root *root) { - lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_lock); return __cset_cgroup_from_root(cset, root); @@ -1453,7 +1460,9 @@ static struct cgroup *cset_cgroup_from_r /* * Return the cgroup for "task" from the given hierarchy. Must be - * called with cgroup_mutex and css_set_lock held. + * called with css_set_lock held to prevent task's groups from being modified. + * Must be called with either cgroup_mutex or rcu read lock to prevent the + * cgroup root from being destroyed. */ struct cgroup *task_cgroup_from_root(struct task_struct *task, struct cgroup_root *root) @@ -2014,7 +2023,7 @@ void init_cgroup_root(struct cgroup_fs_c struct cgroup_root *root = ctx->root; struct cgroup *cgrp = &root->cgrp; - INIT_LIST_HEAD(&root->root_list); + INIT_LIST_HEAD_RCU(&root->root_list); atomic_set(&root->nr_cgrps, 1); cgrp->root = root; init_cgroup_housekeeping(cgrp); @@ -2097,7 +2106,7 @@ int cgroup_setup_root(struct cgroup_root * care of subsystems' refcounts, which are explicitly dropped in * the failure exit path. */ - list_add(&root->root_list, &cgroup_roots); + list_add_rcu(&root->root_list, &cgroup_roots); cgroup_root_count++; /*