From patchwork Tue May 2 13:38:45 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: 13228942 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 E9CDFC77B7E for ; Tue, 2 May 2023 13:39:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234181AbjEBNjt (ORCPT ); Tue, 2 May 2023 09:39:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234101AbjEBNja (ORCPT ); Tue, 2 May 2023 09:39:30 -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 8F30C6E87; Tue, 2 May 2023 06:38:56 -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 D19311FD63; Tue, 2 May 2023 13:38:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1683034729; 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=HAg4rxVkAQ9qbbHiRpMQeKxQl0QBkdUCjNX5t2zLxPg=; b=ucryHQBDna3EZnuiMh3G9y4iAHPKeJYgG5vW3YRNWNx+RmQanqEifFfVPpU4RuNZvgpLzK dMzvFoUWdePAEGbT1Akvg+MJoZuf3pHOAN0HwewEt2EjQLKqfdq4pEq4k4CABGqPdn/hh6 72u9XPh9PqGjmr7yHuob9GzfKzp2ql8= 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 A245C139D2; 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 2MHVJmkSUWTOYQAAMHmgww (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 1/3] cgroup: Drop unused function for cgroup_path Date: Tue, 2 May 2023 15:38:45 +0200 Message-Id: <20230502133847.14570-2-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 There is no current user and there are alternative methods to obtain task's cgroup path. Signed-off-by: Michal Koutný Reviewed-by: Waiman Long --- kernel/cgroup/cgroup.c | 39 --------------------------------------- 1 file changed, 39 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 625d7483951c..55e5f0110e3b 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -2378,45 +2378,6 @@ int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen, } EXPORT_SYMBOL_GPL(cgroup_path_ns); -/** - * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy - * @task: target task - * @buf: the buffer to write the path into - * @buflen: the length of the buffer - * - * Determine @task's cgroup on the first (the one with the lowest non-zero - * hierarchy_id) cgroup hierarchy and copy its path into @buf. This - * function grabs cgroup_mutex and shouldn't be used inside locks used by - * cgroup controller callbacks. - * - * Return value is the same as kernfs_path(). - */ -int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen) -{ - struct cgroup_root *root; - struct cgroup *cgrp; - int hierarchy_id = 1; - int ret; - - cgroup_lock(); - spin_lock_irq(&css_set_lock); - - root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id); - - if (root) { - cgrp = task_cgroup_from_root(task, root); - ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns); - } else { - /* if no hierarchy exists, everyone is in "/" */ - ret = strscpy(buf, "/", buflen); - } - - spin_unlock_irq(&css_set_lock); - cgroup_unlock(); - return ret; -} -EXPORT_SYMBOL_GPL(task_cgroup_path); - /** * cgroup_attach_lock - Lock for ->attach() * @lock_threadgroup: whether to down_write cgroup_threadgroup_rwsem 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. From patchwork Tue May 2 13:38:47 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: 13228943 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 DA324C7EE26 for ; Tue, 2 May 2023 13:39:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234318AbjEBNju (ORCPT ); Tue, 2 May 2023 09:39:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234297AbjEBNjd (ORCPT ); Tue, 2 May 2023 09:39:33 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06FCF6A5E; Tue, 2 May 2023 06:38:58 -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-out1.suse.de (Postfix) with ESMTPS id 3FC7722124; 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=fpw1/CS8jewUjSsdmSx7N0a/briOC9eP8uaWobg+SbE=; b=fE3Cff0u2uDDZoTwPGZOiCHhWMWW2sCmMD5CFUkuzcVoLi2vh0pm8Rwr/uTuKzp8yUeamE ny+LtbLzNp+7qONlp+LrgnBakxzmXydMKFc3U8iqdaukFUOm4Q7DmwqXXxGO0WxmdDOEX8 ka0xGI08HvsuJRFVAK3WDLeiAiUHjZA= 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 10904139D2; Tue, 2 May 2023 13:38:50 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id oDU7A2oSUWTOYQAAMHmgww (envelope-from ); Tue, 02 May 2023 13:38:50 +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 3/3] cgroup: Do not take css_set_lock in cgroup_show_path Date: Tue, 2 May 2023 15:38:47 +0200 Message-Id: <20230502133847.14570-4-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 /proc/$pid/mountinfo may accumulate lots of entries (causing frequent re-reads of whole file) or lots cgroupfs entries alone. The cgroupfs entries rendered with cgroup_show_path() may increase/be subject of css_set_lock contention causing further slowdown -- not only mountinfo rendering but any other css_set_lock user. We leverage the fact that mountinfo reading happens with namespace_sem taken and hierarchy roots thus cannot be freed concurrently. There are three relevant nodes for each cgroupfs entry: R ... cgroup hierarchy root M ... mount root C ... reader's cgroup NS root mountinfo is supposed to show path from C to M. Current's css_set (and linked root cgroups) are stable under namespace_sem, therefore current_cgns_cgroup_from_root() doesn't need css_set_lock. When the path is assembled in kernfs_path_from_node(), we know that: - C kernfs_node is (transitively) pinned via current->nsproxy, - M kernfs_node is pinned thanks to namespace_sem, - path C to M is pinned via child->parent references (this holds also when C and M are in distinct subtrees). Streamline mountinfo rendering a bit by relieving css_set_lock and add careful notes about that. Signed-off-by: Michal Koutný --- kernel/cgroup/cgroup.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 32d693a797b9..e2ec6f0028be 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1407,12 +1407,18 @@ static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset, struct cgroup *res_cgroup = NULL; if (cset == &init_css_set) { + /* callers must ensure root stability */ res_cgroup = &root->cgrp; } else if (root == &cgrp_dfl_root) { res_cgroup = cset->dfl_cgrp; } else { struct cgrp_cset_link *link; - lockdep_assert_held(&css_set_lock); + /* cset's cgroups are pinned unless they are root cgroups that + * were unmounted. We look at links to !cgrp_dfl_root + * cgroup_root, either lock ensures the list is not mutated + */ + lockdep_assert(lockdep_is_held(&css_set_lock) || + lockdep_is_held_type(&namespace_sem, -1)); list_for_each_entry(link, &cset->cgrp_links, cgrp_link) { struct cgroup *c = link->cgrp; @@ -1438,8 +1444,6 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) struct cgroup *res = NULL; struct css_set *cset; - lockdep_assert_held(&css_set_lock); - /* namespace_sem ensures `root` stability on unmount */ lockdep_assert(lockdep_is_held_type(&namespace_sem, -1)); @@ -1905,10 +1909,8 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node, if (!buf) return -ENOMEM; - spin_lock_irq(&css_set_lock); ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot); len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX); - spin_unlock_irq(&css_set_lock); if (len >= PATH_MAX) len = -ERANGE;