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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DEF6CC27C4F for ; Thu, 13 Jun 2024 18:14:46 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=jR/4hRHI; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4W0VtX5Flrz3cTS for ; Fri, 14 Jun 2024 04:14:44 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=jR/4hRHI; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=srs0=qrwz=np=paulmck-thinkpad-p17-gen-1.home=paulmck@kernel.org; receiver=lists.ozlabs.org) Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4W0Vsh3sjMz3cSS for ; Fri, 14 Jun 2024 04:14:00 +1000 (AEST) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 0C8A961CFD; Thu, 13 Jun 2024 18:13:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8EEBC32786; Thu, 13 Jun 2024 18:13:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1718302432; bh=fTIU120VbeRegu4fENGIN2pJl0vJUhORQvgqaO97OJA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=jR/4hRHIvjnr0HuKMd6n8Jn2KplP88ALqz/jBpAKC7iDEoEz5yTd6fMxpCs6goNdu n8elfLSow/niMrJmWbjyCFHbgDgF7GshXU3IoT7xdE5GNXUmv9oEGHq2mjc20rGLwp q0fYO1vllub6LyzhOYauiWoAoj8VOrLrRS7uM4A5UortmkOXNr3XN6j9g1Q0nw5rZI B++vgmEbZiZmvCkQbcm552PFvnT2ReJyoa6yOeebtcW7WCh7SbYjGbpp0bBNshQbGt UgwL7TFo2YOcNsL7tdoefLVWkIgw8OEUPXV25zDiL5YxSslrNLs6bwA797sM/3Spyz ebnTt6JASQjTg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 56F78CE0760; Thu, 13 Jun 2024 11:13:52 -0700 (PDT) Date: Thu, 13 Jun 2024 11:13:52 -0700 From: "Paul E. McKenney" To: Uladzislau Rezki Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback Message-ID: References: <20240609082726.32742-1-Julia.Lawall@inria.fr> <20240612143305.451abf58@kernel.org> <80e03b02-7e24-4342-af0b-ba5117b19828@paulmck-laptop> <7efde25f-6af5-4a67-abea-b26732a8aca1@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Cc: "Jason A. Donenfeld" , kvm@vger.kernel.org, Neil Brown , kernel-janitors@vger.kernel.org, Olga Kornievskaia , Dai Ngo , Christophe Leroy , coreteam@netfilter.org, "Naveen N. Rao" , Jakub Kicinski , linux-trace-kernel@vger.kernel.org, bridge@lists.linux.dev, ecryptfs@vger.kernel.org, Nicholas Piggin , linux-can@vger.kernel.org, linux-block@vger.kernel.org, Mathieu Desnoyers , Vlastimil Babka , Tom Talpey , linux-nfs@vger.kernel.org, netdev@vger.kernel.org, Lai Jiangshan , linux-kernel@vger.kernel.org, Julia Lawall , netfilter-devel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, wireguard@lists.zx2c4.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Jun 13, 2024 at 07:58:17PM +0200, Uladzislau Rezki wrote: > On Thu, Jun 13, 2024 at 10:45:59AM -0700, Paul E. McKenney wrote: > > On Thu, Jun 13, 2024 at 07:38:59PM +0200, Uladzislau Rezki wrote: > > > On Thu, Jun 13, 2024 at 08:06:30AM -0700, Paul E. McKenney wrote: > > > > On Thu, Jun 13, 2024 at 03:06:54PM +0200, Uladzislau Rezki wrote: > > > > > On Thu, Jun 13, 2024 at 05:47:08AM -0700, Paul E. McKenney wrote: > > > > > > On Thu, Jun 13, 2024 at 01:58:59PM +0200, Jason A. Donenfeld wrote: > > > > > > > On Wed, Jun 12, 2024 at 03:37:55PM -0700, Paul E. McKenney wrote: > > > > > > > > On Wed, Jun 12, 2024 at 02:33:05PM -0700, Jakub Kicinski wrote: > > > > > > > > > On Sun, 9 Jun 2024 10:27:12 +0200 Julia Lawall wrote: > > > > > > > > > > Since SLOB was removed, it is not necessary to use call_rcu > > > > > > > > > > when the callback only performs kmem_cache_free. Use > > > > > > > > > > kfree_rcu() directly. > > > > > > > > > > > > > > > > > > > > The changes were done using the following Coccinelle semantic patch. > > > > > > > > > > This semantic patch is designed to ignore cases where the callback > > > > > > > > > > function is used in another way. > > > > > > > > > > > > > > > > > > How does the discussion on: > > > > > > > > > [PATCH] Revert "batman-adv: prefer kfree_rcu() over call_rcu() with free-only callbacks" > > > > > > > > > https://lore.kernel.org/all/20240612133357.2596-1-linus.luessing@c0d3.blue/ > > > > > > > > > reflect on this series? IIUC we should hold off.. > > > > > > > > > > > > > > > > We do need to hold off for the ones in kernel modules (such as 07/14) > > > > > > > > where the kmem_cache is destroyed during module unload. > > > > > > > > > > > > > > > > OK, I might as well go through them... > > > > > > > > > > > > > > > > [PATCH 01/14] wireguard: allowedips: replace call_rcu by kfree_rcu for simple kmem_cache_free callback > > > > > > > > Needs to wait, see wg_allowedips_slab_uninit(). > > > > > > > > > > > > > > Also, notably, this patch needs additionally: > > > > > > > > > > > > > > diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c > > > > > > > index e4e1638fce1b..c95f6937c3f1 100644 > > > > > > > --- a/drivers/net/wireguard/allowedips.c > > > > > > > +++ b/drivers/net/wireguard/allowedips.c > > > > > > > @@ -377,7 +377,6 @@ int __init wg_allowedips_slab_init(void) > > > > > > > > > > > > > > void wg_allowedips_slab_uninit(void) > > > > > > > { > > > > > > > - rcu_barrier(); > > > > > > > kmem_cache_destroy(node_cache); > > > > > > > } > > > > > > > > > > > > > > Once kmem_cache_destroy has been fixed to be deferrable. > > > > > > > > > > > > > > I assume the other patches are similar -- an rcu_barrier() can be > > > > > > > removed. So some manual meddling of these might be in order. > > > > > > > > > > > > Assuming that the deferrable kmem_cache_destroy() is the option chosen, > > > > > > agreed. > > > > > > > > > > > > > > > > void kmem_cache_destroy(struct kmem_cache *s) > > > > > { > > > > > int err = -EBUSY; > > > > > bool rcu_set; > > > > > > > > > > if (unlikely(!s) || !kasan_check_byte(s)) > > > > > return; > > > > > > > > > > cpus_read_lock(); > > > > > mutex_lock(&slab_mutex); > > > > > > > > > > rcu_set = s->flags & SLAB_TYPESAFE_BY_RCU; > > > > > > > > > > s->refcount--; > > > > > if (s->refcount) > > > > > goto out_unlock; > > > > > > > > > > err = shutdown_cache(s); > > > > > WARN(err, "%s %s: Slab cache still has objects when called from %pS", > > > > > __func__, s->name, (void *)_RET_IP_); > > > > > ... > > > > > cpus_read_unlock(); > > > > > if (!err && !rcu_set) > > > > > kmem_cache_release(s); > > > > > } > > > > > > > > > > > > > > > so we have SLAB_TYPESAFE_BY_RCU flag that defers freeing slab-pages > > > > > and a cache by a grace period. Similar flag can be added, like > > > > > SLAB_DESTROY_ONCE_FULLY_FREED, in this case a worker rearm itself > > > > > if there are still objects which should be freed. > > > > > > > > > > Any thoughts here? > > > > > > > > Wouldn't we also need some additional code to later check for all objects > > > > being freed to the slab, whether or not that code is initiated from > > > > kmem_cache_destroy()? > > > > > > > Same away as SLAB_TYPESAFE_BY_RCU is handled from the kmem_cache_destroy() function. > > > It checks that flag and if it is true and extra worker is scheduled to perform a > > > deferred(instead of right away) destroy after rcu_barrier() finishes. > > > > Like this? > > > > SLAB_DESTROY_ONCE_FULLY_FREED > > > > Instead of adding a new kmem_cache_destroy_rcu() > > or kmem_cache_destroy_wait() API member, instead add a > > SLAB_DESTROY_ONCE_FULLY_FREED flag that can be passed to the > > existing kmem_cache_destroy() function.  Use of this flag would > > suppress any warnings that would otherwise be issued if there > > was still slab memory yet to be freed, and it would also spawn > > workqueues (or timers or whatever) to do any needed cleanup work. > > > > > The flag is passed as all others during creating a cache: > > slab = kmem_cache_create(name, size, ..., SLAB_DESTROY_ONCE_FULLY_FREED | OTHER_FLAGS, NULL); > > the rest description is correct to me. Good catch, fixed, thank you! Thanx, Paul