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.zx2c4.com (lists.zx2c4.com [165.227.139.114]) (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 31245C27C79 for ; Fri, 14 Jun 2024 14:50:53 +0000 (UTC) Received: by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTP id 29ebbf56; Fri, 14 Jun 2024 14:50:51 +0000 (UTC) Received: from mail-lf1-x132.google.com (mail-lf1-x132.google.com [2a00:1450:4864:20::132]) by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTPS id 94133e60 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO) for ; Fri, 14 Jun 2024 14:50:49 +0000 (UTC) Received: by mail-lf1-x132.google.com with SMTP id 2adb3069b0e04-52c89d6b4adso2112462e87.3 for ; Fri, 14 Jun 2024 07:50:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1718376649; x=1718981449; darn=lists.zx2c4.com; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:date:from:from:to :cc:subject:date:message-id:reply-to; bh=A1vDM+/434Vy7O2My5RlGhyPzc53w2jNpv2mu0lM6fk=; b=b1BQq9gMWrOmcYluMsImyynmnPcmf+GVs0NJhqkqGyQXUQxt/2j65ZKKqK2X8iMTyu t0KcjmWnz0Xpv+Plvu9AgvOl9CfVWlbjm0kmdB/YlqKLS7efy9jxFRXgskFV0uZVftZU cEAV2HU9+xnzW1quewQthXSeKirMKMFPVZ+WBH+TlwaoBVY1tztxg7hb77hmLjc7oqQg 4eBYOP1WpAc+lM4V1br4mX2FfLMBIcXhge1YmZEO9LDolTexBlgVgt/lS5CrxnsrBcCt 3VGgTbjZOORZehDQri7915d1FEiVOGZiwfWFywkxBkemkv+NzczJYIEHUmHUfk2xcXPA sW0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1718376649; x=1718981449; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:date:from :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=A1vDM+/434Vy7O2My5RlGhyPzc53w2jNpv2mu0lM6fk=; b=ZzLZxuVvGrD+8xXqbgOlLJFZwek3G5lRWRqXdJjt9jjKOvCxH11shGE1jxJpijKHu/ ZQF7AUliNU7y0rj8vTAJyFjs1O9gw+TgBKt8VQZWPIwO2BT84ciD/IJI/viuchBoLmbO mVg/8RsEuR9Q8ovxvIhRx0CpCpGgVvZ10KhcTVavvS24wUsp2e8Xm10zZKZolFVuMRmA wQ5Z+xMlGgNQhswhOcU5oBDY/HFL40Dv6+/81BU1layO3wimD+UMBg5HqG155/4/IwYD q4rbbJ+BY79LXItZQNxdwpTZoV32KCo10XR5a8YkhFYgpNZwok0Kc1LVq8lX9FUkYTst ZQMQ== X-Forwarded-Encrypted: i=1; AJvYcCXdlBMCrcFP+G1SpuDsdFJun0vBu7VzMAx3TXccyQJ/nOVqhudu+hywcQeIYNdWjC3RL4qlZwi6mxGNuW1Q+uyFGL0zRQvx1omO X-Gm-Message-State: AOJu0Yw+hWgkp7cCFxMyAYx9NuJV/CKqltftJeEgMWRwh1XggTDU9Kgj 4jxLYIbJWSBXvJiqhpZwUXRLuIA0rtjD+BSz1QSUJJATZ2bdDmpv X-Google-Smtp-Source: AGHT+IFwcocbKCVljpVcKX91E2mKCvIpm5pfUWDi+eXb482Grpw2w/2u1FYYW0LUN48bweJbaljbrg== X-Received: by 2002:ac2:4181:0:b0:52c:a5e6:989e with SMTP id 2adb3069b0e04-52ca6e656d3mr1989889e87.16.1718376648691; Fri, 14 Jun 2024 07:50:48 -0700 (PDT) Received: from pc636 (host-90-233-218-141.mobileonline.telia.com. [90.233.218.141]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-52ca2888119sm534327e87.266.2024.06.14.07.50.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Jun 2024 07:50:48 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Fri, 14 Jun 2024 16:50:45 +0200 To: "Paul E. McKenney" Cc: Uladzislau Rezki , Vlastimil Babka , "Jason A. Donenfeld" , Jakub Kicinski , Julia Lawall , linux-block@vger.kernel.org, kernel-janitors@vger.kernel.org, bridge@lists.linux.dev, linux-trace-kernel@vger.kernel.org, Mathieu Desnoyers , kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Naveen N. Rao" , Christophe Leroy , Nicholas Piggin , netdev@vger.kernel.org, wireguard@lists.zx2c4.com, linux-kernel@vger.kernel.org, ecryptfs@vger.kernel.org, Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org, linux-can@vger.kernel.org, Lai Jiangshan , netfilter-devel@vger.kernel.org, coreteam@netfilter.org Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback Message-ID: References: <80e03b02-7e24-4342-af0b-ba5117b19828@paulmck-laptop> <7efde25f-6af5-4a67-abea-b26732a8aca1@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: wireguard@lists.zx2c4.com X-Mailman-Version: 2.1.30rc1 Precedence: list List-Id: Development discussion of WireGuard List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: wireguard-bounces@lists.zx2c4.com Sender: "WireGuard" On Fri, Jun 14, 2024 at 07:17:29AM -0700, Paul E. McKenney wrote: > On Fri, Jun 14, 2024 at 02:35:33PM +0200, Uladzislau Rezki wrote: > > On Thu, Jun 13, 2024 at 11:13:52AM -0700, Paul E. McKenney wrote: > > > 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! > > > > > And here we go with prototype(untested): > > Thank you for putting this together! It looks way simpler than I would > have guessed, and quite a bit simpler than I would expect it would be > to extend rcu_barrier() to cover kfree_rcu(). > Yep, it should be pretty pretty straightforward. The slab mechanism does not have a functionality when it comes to defer of destroying, i.e. it is not allowed to destroy non-fully-freed-slab: void kmem_cache_destroy(struct kmem_cache *s) { ... err = shutdown_cache(s); WARN(err, "%s %s: Slab cache still has objects when called from %pS", __func__, s->name, (void *)_RET_IP_); ... So, this patch extends it. > > > > +static void > > +slab_caches_defer_destroy_workfn(struct work_struct *work) > > +{ > > + struct kmem_cache *s, *s2; > > + > > + mutex_lock(&slab_mutex); > > + list_for_each_entry_safe(s, s2, &slab_caches_defer_destroy, list) { > > + if (__kmem_cache_empty(s)) { > > + /* free asan quarantined objects */ > > + kasan_cache_shutdown(s); > > + (void) __kmem_cache_shutdown(s); > > + > > + list_del(&s->list); > > + > > + debugfs_slab_release(s); > > + kfence_shutdown_cache(s); > > + kmem_cache_release(s); > > + } > > My guess is that there would want to be a splat if the slab stuck around > for too long, but maybe that should instead be handled elsewhere or in > some other way? I must defer to you guys on that one. > Probably yes. -- Uladzislau Rezki