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 768C81EF083; Tue, 15 Oct 2024 11:40:20 +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=1728992420; cv=none; b=h529yoWExYc/b1ybnjE9UhyF68KoY9X4O5gXmSNO5LUVnmZ+OigOW6ylXYRTCD3giw2akwaLlVOWw1Owb04pTjLhtBjUGmI5RBBRVp+HWXQoSobdoS3cdIdD4K9BQSAugP+uKNeMX8bDFl0M2UnmCcfYq/VYPxEaP/htSWQ0F5c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728992420; c=relaxed/simple; bh=p96rqc3xYj8zh3Rd0hYorhDlszX0M8KCKNqqiIdDqvI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bvXZ4mce9++cvhpx2TK5A7Tu1caG13wQeDAYG5+I61KoqUDWp2SjfUnGpl1L7OdcHIdKB2BikJXpfzXUPUbj6hoeiRWtkZ4NOpHOYYtGof8Vz/W5sAJgcTMhEMYRXoW/7SZvuKKmd5lK5VHa7LAh76DuYLjYUPM2lCn4g5WT3sA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jdT0FmjD; 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="jdT0FmjD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF338C4CEC6; Tue, 15 Oct 2024 11:40:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1728992420; bh=p96rqc3xYj8zh3Rd0hYorhDlszX0M8KCKNqqiIdDqvI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jdT0FmjDMP8PX0xrnTEoTukRBqkIf5svW9Ypxor4I8TWGXiKnvt43aoQ4DPrpeo3j pOxvqVLLMemogcDn0MYYo7jHqL2RuhNT/OI+w0Pqc4zeXiw/FHHdfEc3zc8+bLc/rf 5aHm/JlmYnIwGU3y02MGZSbl6y5fgBnNq1sawEgc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yafang Shao , Tejun Heo , Sasha Levin Subject: [PATCH 5.15 080/691] cgroup: Make operations on the cgroup root_list RCU safe Date: Tue, 15 Oct 2024 13:20:28 +0200 Message-ID: <20241015112443.532007991@linuxfoundation.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241015112440.309539031@linuxfoundation.org> References: <20241015112440.309539031@linuxfoundation.org> User-Agent: quilt/0.67 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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yafang Shao [ Upstream commit d23b5c577715892c87533b13923306acc6243f93 ] 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 Signed-off-by: Sasha Levin --- include/linux/cgroup-defs.h | 1 + kernel/cgroup/cgroup-internal.h | 3 ++- kernel/cgroup/cgroup.c | 14 +++++++------- 3 files changed, 10 insertions(+), 8 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index cd8b8bd5ec4d5..61e92fd055d9c 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -516,6 +516,7 @@ 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; diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h index d8fcc139ac05d..f38f56b8cc416 100644 --- a/kernel/cgroup/cgroup-internal.h +++ b/kernel/cgroup/cgroup-internal.h @@ -172,7 +172,8 @@ 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 diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 84e85561a87c0..999fef6d12282 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1332,7 +1332,7 @@ static void cgroup_exit_root_id(struct cgroup_root *root) void cgroup_free_root(struct cgroup_root *root) { - kfree(root); + kfree_rcu(root, rcu); } static void cgroup_destroy_root(struct cgroup_root *root) @@ -1365,7 +1365,7 @@ static void cgroup_destroy_root(struct cgroup_root *root) 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--; } @@ -1411,7 +1411,6 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) } rcu_read_unlock(); - BUG_ON(!res); return res; } @@ -1421,7 +1420,6 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset, { struct cgroup *res = NULL; - lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_lock); if (cset == &init_css_set) { @@ -1447,7 +1445,9 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset, /* * 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) @@ -1986,7 +1986,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx) 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); @@ -2068,7 +2068,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask) * 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++; /* -- 2.43.0