From patchwork Fri Jan 27 01:15:35 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rik van Riel X-Patchwork-Id: 13118025 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 102CFC54EAA for ; Fri, 27 Jan 2023 01:15:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232835AbjA0BPx (ORCPT ); Thu, 26 Jan 2023 20:15:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229844AbjA0BPu (ORCPT ); Thu, 26 Jan 2023 20:15:50 -0500 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB7836F223; Thu, 26 Jan 2023 17:15:49 -0800 (PST) Received: from imladris.home.surriel.com ([10.0.13.28] helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1pLDLC-00038z-2y; Thu, 26 Jan 2023 20:15:42 -0500 From: Rik van Riel To: viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org, kernel-team@meta.com, linux-fsdevel@vger.kernel.org, gscrivan@redhat.com Cc: Rik van Riel , Chris Mason Subject: [PATCH 2/2] ipc,namespace: batch free ipc_namespace structures Date: Thu, 26 Jan 2023 20:15:35 -0500 Message-Id: <20230127011535.1265297-3-riel@surriel.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20230127011535.1265297-1-riel@surriel.com> References: <20230127011535.1265297-1-riel@surriel.com> MIME-Version: 1.0 Sender: riel@shelob.surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Instead of waiting for an RCU grace period between each ipc_namespace structure that is being freed, wait an RCU grace period for every batch of ipc_namespace structures. Thanks to Al Viro for the suggestion of the helper function. This speeds up the run time of the test case that allocates ipc_namespaces in a loop from 6 minutes, to a little over 1 second: real 0m1.192s user 0m0.038s sys 0m1.152s Signed-off-by: Rik van Riel Reported-by: Chris Mason Suggested-by: Al Viro --- fs/namespace.c | 10 ++++++++++ include/linux/mount.h | 1 + ipc/namespace.c | 13 ++++++++++--- 3 files changed, 21 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index ab467ee58341..296432ba3716 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1397,6 +1397,16 @@ struct vfsmount *mntget(struct vfsmount *mnt) } EXPORT_SYMBOL(mntget); +/* + * Make a mount point inaccessible to new lookups. + * Because there may still be current users, the caller MUST WAIT + * for an RCU grace period before destroying the mount point. + */ +void mnt_make_shortterm(struct vfsmount *mnt) +{ + real_mount(mnt)->mnt_ns = NULL; +} + /** * path_is_mountpoint() - Check if path is a mount in the current namespace. * @path: path to check diff --git a/include/linux/mount.h b/include/linux/mount.h index 62475996fac6..ec55a031aa8c 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -88,6 +88,7 @@ extern void mnt_drop_write(struct vfsmount *mnt); extern void mnt_drop_write_file(struct file *file); extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); +extern void mnt_make_shortterm(struct vfsmount *mnt); extern struct vfsmount *mnt_clone_internal(const struct path *path); extern bool __mnt_is_readonly(struct vfsmount *mnt); extern bool mnt_may_suid(struct vfsmount *mnt); diff --git a/ipc/namespace.c b/ipc/namespace.c index a26860a41dac..6ecc30effd3e 100644 --- a/ipc/namespace.c +++ b/ipc/namespace.c @@ -145,10 +145,11 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids, static void free_ipc_ns(struct ipc_namespace *ns) { - /* mq_put_mnt() waits for a grace period as kern_unmount() - * uses synchronize_rcu(). + /* + * Caller needs to wait for an RCU grace period to have passed + * after making the mount point inaccessible to new accesses. */ - mq_put_mnt(ns); + mntput(ns->mq_mnt); sem_exit_ns(ns); msg_exit_ns(ns); shm_exit_ns(ns); @@ -168,6 +169,12 @@ static void free_ipc(struct work_struct *unused) struct llist_node *node = llist_del_all(&free_ipc_list); struct ipc_namespace *n, *t; + llist_for_each_entry_safe(n, t, node, mnt_llist) + mnt_make_shortterm(n->mq_mnt); + + /* Wait for any last users to have gone away. */ + synchronize_rcu(); + llist_for_each_entry_safe(n, t, node, mnt_llist) free_ipc_ns(n); }