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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8CB6ECAAD8 for ; Thu, 1 Sep 2022 15:43:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232065AbiIAPnn (ORCPT ); Thu, 1 Sep 2022 11:43:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40990 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232994AbiIAPnf (ORCPT ); Thu, 1 Sep 2022 11:43:35 -0400 Received: from out1.migadu.com (out1.migadu.com [91.121.223.63]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5E261719AC; Thu, 1 Sep 2022 08:43:31 -0700 (PDT) Date: Thu, 1 Sep 2022 11:43:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1662047009; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=OCuFL4N5GVZjONQAdChOE7OJr7ThTUJDCIIbzLkwFEk=; b=Zug2Ft4Qd/net99BOTd8W8Yfuju//gSHL3gkzYXZLEVciKsEhf1UkIyXgrPgVXlVt/CoSK WIJngXjsqZ/WvBYvq+hwDukTtw4VIC1L39QDy0ARuz5vTfzc62/XGVpvD13hkozhflqLO3 W0o6TaATn9DtFDXStAFl/opHuur0FVU= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kent Overstreet To: Steven Rostedt Cc: Peter Zijlstra , Suren Baghdasaryan , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, void@manifault.com, juri.lelli@redhat.com, ldufour@linux.ibm.com, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, arnd@arndb.de, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-mm@kvack.org, iommu@lists.linux.dev, kasan-dev@googlegroups.com, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 03/30] Lazy percpu counters Message-ID: <20220901154321.apyq7246srkjthfr@moria.home.lan> References: <20220830214919.53220-1-surenb@google.com> <20220830214919.53220-4-surenb@google.com> <20220901143219.n7jg7cbp47agqnwn@moria.home.lan> <20220901104839.5691e1c9@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220901104839.5691e1c9@gandalf.local.home> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Sep 01, 2022 at 10:48:39AM -0400, Steven Rostedt wrote: > On Thu, 1 Sep 2022 10:32:19 -0400 > Kent Overstreet wrote: > > > On Thu, Sep 01, 2022 at 08:51:31AM +0200, Peter Zijlstra wrote: > > > On Tue, Aug 30, 2022 at 02:48:52PM -0700, Suren Baghdasaryan wrote: > > > > +static void lazy_percpu_counter_switch_to_pcpu(struct raw_lazy_percpu_counter *c) > > > > +{ > > > > + u64 __percpu *pcpu_v = alloc_percpu_gfp(u64, GFP_ATOMIC|__GFP_NOWARN); > > > > > > Realize that this is incorrect when used under a raw_spinlock_t. > > > > Can you elaborate? > > All allocations (including GFP_ATOMIC) grab normal spin_locks. When > PREEMPT_RT is configured, normal spin_locks turn into a mutex, where as > raw_spinlock's do not. > > Thus, if this is done within a raw_spinlock with PREEMPT_RT configured, it > can cause a schedule while holding a spinlock. Thanks, I think we should be good here but I'll document it anyways.