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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 ADE65C433DF for ; Tue, 11 Aug 2020 16:02:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DD0220774 for ; Tue, 11 Aug 2020 16:02:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597161761; bh=qYjAEv7PFjicCivlNg27thPuwsPSl2pW3y8n1g52xbo=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=NfZBVWhZw/27d5bCfRR3WQhM4FdSrI2I7VWkxV1Upd8yCEA3K1blHm9s07yPwg7ka 2TlypBqPoVdXvs1lO85GaCOHCIWmbY4IpPVzZRi6j7loWU/m/z66Sw5rZNRND+xDYu c9DzTxkGArcOWcKeGZ4urxCEtT3Itgc6wJc3AtlI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728906AbgHKQCl (ORCPT ); Tue, 11 Aug 2020 12:02:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:55650 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728797AbgHKQCl (ORCPT ); Tue, 11 Aug 2020 12:02:41 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7AE43206B5; Tue, 11 Aug 2020 16:02:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597161760; bh=qYjAEv7PFjicCivlNg27thPuwsPSl2pW3y8n1g52xbo=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=YMO9U9SrhWMqJ6Y4HH/o0t7jAj1v65S7N2JlARf6q5vk+yTw10TcbKsWrFi0sbozy O6j38JkiSunsI5C87fE57P9EHHElsQnmLANlxkeb5HDe0ihvKhM4kg+XB1Z+LjlQrE +uQkxPr4g1nS0SCJtW87TfgCEwh+w9ku1x7Ykdt0= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5BC5D352308E; Tue, 11 Aug 2020 09:02:40 -0700 (PDT) Date: Tue, 11 Aug 2020 09:02:40 -0700 From: "Paul E. McKenney" To: Thomas Gleixner 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 Message-ID: <20200811160240.GX4295@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87h7t96ve3.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Tue, Aug 11, 2020 at 05:43:16PM +0200, Thomas Gleixner wrote: > "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? Some BPF code that needs to process and free a list. As noted above, this is a patch rather than something that is already in mainline. Not surprising, though, given call_rcu() invocations in similar contexts. Yes, we can perhaps rework all current and future callers to avoid invoking both call_rcu() and kfree_rcu() from raw atomic context, but the required change to permit this is quite a bit simpler. Thanx, Paul