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 B982B6F2FE; Thu, 12 Dec 2024 17:43:57 +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=1734025437; cv=none; b=YEx2yC+R3cGj5mi0JbRwv2nPF65P3tZyL/nBJz1DEurYwdX1M+0mBRals9cJEv2GJqeQsOPm1En/km0PYyE7ZCqYf2bTbSAMSdX6WdZi4OsqIyHyY63bRKKBuHWPJ1JINRnJxUP6XoZeGxMopGKNwwEBk59L14d4h1NFZ2RuObw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734025437; c=relaxed/simple; bh=COm7bFt8dkceTYiiHKBCoCLn5oJQf/RkVbfFaVLWEUU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rHN6JN4+icao6J5aFVxJFsrD8iMSvlw1h3jAQ7Jvr77yKsaFj0rahQFst01auA6EtxwXpkQ+xipbzhqmRLRzAd39CpHCtm6knnMxpa0YYyghS6SFecRXPAZOB0QGurD2rQ6kGrr+aKg164B/+mZG8vByS2wx41uPaBDOk9VoB4w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fMCc2Uk5; 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="fMCc2Uk5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AE83C4CECE; Thu, 12 Dec 2024 17:43:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1734025437; bh=COm7bFt8dkceTYiiHKBCoCLn5oJQf/RkVbfFaVLWEUU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fMCc2Uk5vIO4VwQ8/c0+SQ3o2i94YrK6mldxuiZrdtF0Q4mwxYxEnyaqcMIaS/fod Ecmv32Usx7wW9A0Jo9rmqYaJrTzm11MhDCxJqTb8cxDFDpeQK04QgcxBJMtDJ34FzH BPZHx30NUhkr8gHN7zAPjCY+GvubYXs1gA2unFKU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yafang Shao , Tejun Heo , Fedor Pchelkin , Shivani Agarwal , Siddh Raman Pant Subject: [PATCH 5.4 142/321] cgroup: Make operations on the cgroup root_list RCU safe Date: Thu, 12 Dec 2024 16:01:00 +0100 Message-ID: <20241212144235.586996883@linuxfoundation.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20241212144229.291682835@linuxfoundation.org> References: <20241212144229.291682835@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-Transfer-Encoding: 8bit 5.4-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 [fp: adapt to 5.10 mainly because of changes made by e210a89f5b07 ("cgroup.c: add helper __cset_cgroup_from_root to cleanup duplicated codes")] Signed-off-by: Fedor Pchelkin [Shivani: Modified to apply on v5.4.y] Signed-off-by: Shivani Agarwal Reviewed-by: Siddh Raman Pant Signed-off-by: Siddh Raman Pant 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 @@ -517,6 +517,7 @@ 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 @@ -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 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1314,7 +1314,7 @@ void cgroup_free_root(struct cgroup_root { if (root) { idr_destroy(&root->cgroup_idr); - kfree(root); + kfree_rcu(root, rcu); } } @@ -1348,7 +1348,7 @@ 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--; } @@ -1401,7 +1401,6 @@ static struct cgroup *cset_cgroup_from_r { struct cgroup *res = NULL; - lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_lock); if (cset == &init_css_set) { @@ -1421,13 +1420,23 @@ static struct cgroup *cset_cgroup_from_r } } - BUG_ON(!res); + /* + * 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; } /* * 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) @@ -2012,7 +2021,7 @@ 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); @@ -2094,7 +2103,7 @@ 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++; /*