From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA7E2C34024 for ; Mon, 17 Feb 2020 18:08:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99D2120725 for ; Mon, 17 Feb 2020 18:08:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581962891; bh=eJZ8DT4ReB2j3gXDW52rcZiaKWlX7eBGNI/gI1+FkEw=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=zTKf4Dx/xDglYuFMpYWeyD+zRxpG1U8wk3/kTQffvKQdIMbdq1m41KUSeDv0iSAYR AcP2gWoEcdKe4Z7ZNsvQ/iUxFAz1T7xaz+ctb1rb/1RcCme1F367RANHqQl8N3zIG0 /CkOWWVO/0Pm9QgrGPytW+mNMYaSBaBIsKSHQdPg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729829AbgBQSIK (ORCPT ); Mon, 17 Feb 2020 13:08:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:35676 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726707AbgBQSIK (ORCPT ); Mon, 17 Feb 2020 13:08:10 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 44D6B2070B; Mon, 17 Feb 2020 18:08:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581962889; bh=eJZ8DT4ReB2j3gXDW52rcZiaKWlX7eBGNI/gI1+FkEw=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=pMg2Ax8i/SXBAocIAn2rTrkbCEZJ9twN8uoojQWM4IjNClmN3U1wfSkhuyRgkKSYf A8dNM0oLWS5TQD5Y1lJ/HVUJ8Y9xZUKwhi2kmJRHpdqSPvoM+QcstVqLH7+aepRtkJ 5VImKj9JDXYfrKsxtHqHFBBIlIj2dX3IhXumGpT4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 1F1BB352273C; Mon, 17 Feb 2020 10:08:09 -0800 (PST) Date: Mon, 17 Feb 2020 10:08:09 -0800 From: "Paul E. McKenney" To: Giuseppe Scrivano Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, ebiederm@xmission.com Subject: Re: [PATCH] ipc: use a work queue to free_ipc Message-ID: <20200217180809.GO2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200211162408.2194037-1-gscrivan@redhat.com> <20200216141151.GJ2935@paulmck-ThinkPad-P72> <875zg5r2ih.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875zg5r2ih.fsf@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 17, 2020 at 10:23:18AM +0100, Giuseppe Scrivano wrote: > Hi Paul, > > "Paul E. McKenney" writes: > > > Nice speedup! > > > > However, I am not convinced that the code shown below is safe. > > > > I believe that you need either a synchronize_rcu() in your free_ipc() > > function or that you need to pass free_ipc() to queue_rcu_work() instead > > of directly schedule_work(). As things are, I would expect you to see > > free_ipc_ns() being invoke too soon on heavily loaded CONFIG_PREEMPT=y > > kernels. Which can be quite a pain to debug! > > > > Or am I missing something? > > thanks for the review! > > Would being called too soon be a problem? The current version calls > free_ipc_ns() as part of the put_ipc_ns cleanup. > > free_ipc() calls immediately synchronize_rcu() through free_ipc_ns(): > > free_ipc_ns() -> mq_put_mnt() -> kern_unmount() -> synchronize_rcu() Ah, I did not look deeply enough. > Do you think we should make it more explicit and add a synchronize_rcu() > as part of the free_ipc_ns() function itself? Maybe just a comment on the free_ipc_ns() saying that it waits for a grace period. Thanx, Paul > Regards, > Giuseppe > > > > > > Thanx, Paul > > > >> Signed-off-by: Giuseppe Scrivano > >> --- > >> include/linux/ipc_namespace.h | 2 ++ > >> ipc/namespace.c | 17 +++++++++++++++-- > >> 2 files changed, 17 insertions(+), 2 deletions(-) > >> > >> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h > >> index c309f43bde45..a06a78c67f19 100644 > >> --- a/include/linux/ipc_namespace.h > >> +++ b/include/linux/ipc_namespace.h > >> @@ -68,6 +68,8 @@ struct ipc_namespace { > >> struct user_namespace *user_ns; > >> struct ucounts *ucounts; > >> > >> + struct llist_node mnt_llist; > >> + > >> struct ns_common ns; > >> } __randomize_layout; > >> > >> diff --git a/ipc/namespace.c b/ipc/namespace.c > >> index b3ca1476ca51..37d27e1b807a 100644 > >> --- a/ipc/namespace.c > >> +++ b/ipc/namespace.c > >> @@ -117,6 +117,7 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids, > >> > >> static void free_ipc_ns(struct ipc_namespace *ns) > >> { > >> + mq_put_mnt(ns); > >> sem_exit_ns(ns); > >> msg_exit_ns(ns); > >> shm_exit_ns(ns); > >> @@ -127,6 +128,17 @@ static void free_ipc_ns(struct ipc_namespace *ns) > >> kfree(ns); > >> } > >> > >> +static LLIST_HEAD(free_ipc_list); > >> +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) > >> + free_ipc_ns(n); > >> +} > >> +static DECLARE_WORK(free_ipc_work, free_ipc); > >> + > >> /* > >> * put_ipc_ns - drop a reference to an ipc namespace. > >> * @ns: the namespace to put > >> @@ -148,8 +160,9 @@ void put_ipc_ns(struct ipc_namespace *ns) > >> if (refcount_dec_and_lock(&ns->count, &mq_lock)) { > >> mq_clear_sbinfo(ns); > >> spin_unlock(&mq_lock); > >> - mq_put_mnt(ns); > >> - free_ipc_ns(ns); > >> + > >> + if (llist_add(&ns->mnt_llist, &free_ipc_list)) > >> + schedule_work(&free_ipc_work); > >> } > >> } > >> > >> -- > >> 2.24.1 > >> >