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=-12.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 4AE55C4338F for ; Fri, 23 Jul 2021 22:40:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 242DD60F26 for ; Fri, 23 Jul 2021 22:40:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232942AbhGWV7W (ORCPT ); Fri, 23 Jul 2021 17:59:22 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:46200 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231954AbhGWV7U (ORCPT ); Fri, 23 Jul 2021 17:59:20 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 956E220003; Fri, 23 Jul 2021 22:39:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1627079992; 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=QbWYyES6yS++/mUvpq0fraCgAR+v/Vi0waf2hTVIYvE=; b=gm4Qunmbzdnr9wPkLmyedqU1KtOn4+1yS2bGlDPXRzPVS/lUQjPPfKT3lptFQxEkC1aD1P +UiqP46Ki9fsxQjOUCBcKc/Ig1/2kuyiF16c8q73hU0xgEVkCZBKaGYxjHaDLYgM140OXH Owo6QPc7gV5vCzhJrEAE3jJhSkrilCk= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1627079992; 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=QbWYyES6yS++/mUvpq0fraCgAR+v/Vi0waf2hTVIYvE=; b=kntTgiACfht19gsWcNjjszTL3IcuWcYSUi2FWfZYENqmKBqHAA1FNc1lH9DtLWYh7GZWn6 xdexpDdbl3s9s9CA== Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 imap1.suse-dmz.suse.de (Postfix) with ESMTPS id 6A69713697; Fri, 23 Jul 2021 22:39:52 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id MjSEGDhF+2CHBQAAGKfGzw (envelope-from ); Fri, 23 Jul 2021 22:39:52 +0000 Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope To: Mike Galbraith , Thomas Gleixner , LKML Cc: linux-rt-users@vger.kernel.org, Mel Gorman , Sebastian Andrzej Siewior References: <87tul5p2fa.ffs@nanos.tec.linutronix.de> <8c0e0c486056b5185b58998f2cce62619ed3f05c.camel@gmx.de> <878s2fnv79.ffs@nanos.tec.linutronix.de> <6c0e20dd84084036d5068e445746c3ed7e82ec4b.camel@gmx.de> <7431ceb9761c566cf2d1f6f263247acd8d38c4b5.camel@gmx.de> <240f104fc6757d8c38fa01342511eda931632d5a.camel@gmx.de> <69da2ecd-a797-e264-fbfa-13108dc7a573@suse.cz> <84a7bd02cf109c6a5a8c7cc2bfc2898cb98270aa.camel@gmx.de> From: Vlastimil Babka Message-ID: <5be1a703-9a0a-4115-1d69-634e5e8ecefd@suse.cz> Date: Sat, 24 Jul 2021 00:39:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <84a7bd02cf109c6a5a8c7cc2bfc2898cb98270aa.camel@gmx.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/21/21 11:33 AM, Mike Galbraith wrote: > On Wed, 2021-07-21 at 10:44 +0200, Vlastimil Babka wrote: >> >> So this doesn't look like our put_cpu_partial() preempted a >> __slab_alloc() on the same cpu, right? > > No, likely it was the one preempted by someone long gone, but we'll > never know without setting a trap. > >> BTW did my ugly patch work? > > Nope. I guess you missed my reporting it to have been a -ENOBOOT, and Indeed, I misunderstood it as you talking about your patch. > that cutting it in half, ie snagging only __slab_free() does boot, and > seems to cure all of the RT fireworks. OK, so depending on drain=1 makes this apply only to put_cpu_partial() called from __slab_free and not get_partial_node(). One notable difference is that in __slab_free we don't have n->list_lock locked and in get_partial_node() we do. I guess in case your list_lock is made raw again by another patch, that explains a local_lock can't nest under it. If not, then I would expect this to work (I don't think they ever nest in the opposite order, also lockdep should tell us instead of -ENOBOOT?), but might be missing something... I'd rather not nest those locks in any case. I just need to convince myself that the scenario the half-fix fixes is indeed the only one that's needed and we're not leaving there other races that are just harder to trigger... > (chainsaw noises...) > > --- > mm/slub.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2551,6 +2551,8 @@ static void put_cpu_partial(struct kmem_ > int pobjects; > > slub_get_cpu_ptr(s->cpu_slab); > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain) > + local_lock(&s->cpu_slab->lock); > do { > pages = 0; > pobjects = 0; > @@ -2564,7 +2566,13 @@ static void put_cpu_partial(struct kmem_ > * partial array is full. Move the existing > * set to the per node partial list. > */ > - unfreeze_partials(s); > + this_cpu_write(s->cpu_slab->partial, NULL); > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain) > + local_unlock(&s->cpu_slab->lock); > + __unfreeze_partials(s, oldpage); > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain) > + local_lock(&s->cpu_slab->lock); > + > oldpage = NULL; > pobjects = 0; > pages = 0; > @@ -2581,6 +2589,8 @@ static void put_cpu_partial(struct kmem_ > > } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) > != oldpage); > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain) > + local_unlock(&s->cpu_slab->lock); > slub_put_cpu_ptr(s->cpu_slab); > #endif /* CONFIG_SLUB_CPU_PARTIAL */ > } > >