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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 B0373C433DF for ; Tue, 11 Aug 2020 19:39:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AB9D206B2 for ; Tue, 11 Aug 2020 19:39:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="oHAMia7u"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="5elTrME8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726420AbgHKTjN (ORCPT ); Tue, 11 Aug 2020 15:39:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726405AbgHKTjN (ORCPT ); Tue, 11 Aug 2020 15:39:13 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 000E6C06174A; Tue, 11 Aug 2020 12:39:12 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1597174751; 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=YV8vEVVqhngk6zTeFdnzvuc65En/mdSLGrqYDqzVMCg=; b=oHAMia7usYnGV2/RbJIvgRIFvUXvTG1MqS0jAZdgAYOx9M5ro+TzckijDUADM/SInRXrBu 1yimeOxa2NVEiVIHyprnRi6fmMg70374QzA7yoCp1Z1SoI63nUOztGCJ96Igb+JvIzLbhY hiI7wFKn0tQHZYgCctYnvTUDNklRkGAcYx40u5JdzPIfoGgBrjzxO13tnzBMhEazDVNSBu rq0y/UtPS2S5Cx46Ys3AJTHEx6OBXd9Bg+7Fx1Rn2EmpoXclNR04sva/VVv/sltViSdJpS tb8OOxICpLyHsfimC7Stucm4e25ujHgSWW043c+a9AhmPQ9cO1De+PFSHy0gTQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1597174751; 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=YV8vEVVqhngk6zTeFdnzvuc65En/mdSLGrqYDqzVMCg=; b=5elTrME8Ulv5SlkhoPEmX3f8GciJjnw7jNzCPNSl2o6RnBtKEsfmk+OiBO4Fxx9XgSgzbM sC9NgOyDeRXNApBw== To: paulmck@kernel.org Cc: Michal Hocko , Uladzislau Rezki , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag In-Reply-To: <87h7t96ve3.fsf@nanos.tec.linutronix.de> References: <20200809204354.20137-1-urezki@gmail.com> <20200809204354.20137-2-urezki@gmail.com> <20200810123141.GF4773@dhcp22.suse.cz> <20200810160739.GA29884@pc636> <20200810192525.GG4773@dhcp22.suse.cz> <87pn7x6y4a.fsf@nanos.tec.linutronix.de> <20200811153327.GW4295@paulmck-ThinkPad-P72> <87h7t96ve3.fsf@nanos.tec.linutronix.de> Date: Tue, 11 Aug 2020 21:39:10 +0200 Message-ID: <87eeod6kgx.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Thomas Gleixner writes: > "Paul E. McKenney" writes: >> On Tue, Aug 11, 2020 at 04:44:21PM +0200, Thomas Gleixner wrote: >>> Now RCU creates a new thing which enforces to make page allocation in >>> atomic context possible on RT. What for? >>> >>> What's the actual use case in truly atomic context for this new thing on >>> an RT kernel? >> >> It is not just RT kernels. CONFIG_PROVE_RAW_LOCK_NESTING=y propagates >> this constraint to all configurations, and a patch in your new favorite >> subsystem really did trigger this lockdep check in a non-RT kernel. >> >>> The actual RCU code disabling interrupts is an implementation detail >>> which can easily be mitigated with a local lock. >> >> In this case, we are in raw-spinlock context on entry to kfree_rcu(). > > Where? And aside of the where, wasn't kfree_rcu() from within raw spinlock held regions possible all the time? Either I'm missing something or you are fundamentally changing RCU internals. kfree_rcu() saved RT in various ways where invoking kfree() was just not an option. Confused... Thanks, tglx