From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751821AbdIENbJ (ORCPT ); Tue, 5 Sep 2017 09:31:09 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:45565 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751617AbdIENbH (ORCPT ); Tue, 5 Sep 2017 09:31:07 -0400 Date: Tue, 5 Sep 2017 15:31:02 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] smp/hotplug annotations In-Reply-To: <20170905075218.526515965@infradead.org> Message-ID: References: <20170905075218.526515965@infradead.org> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 5 Sep 2017, Peter Zijlstra wrote: > These two patches appear to make hotplug work again without tripping lockdep. They cover the case where the plug/unplug succeeds, but they will not work when a plug/unplug operation fails, because after a fail it rolls back automatically, so in case UP fails, it will go down again, but the initiator side still waits on the 'UP' completion. Same issue on down. I think that extra lockdep magic can be avoided completely by splitting the completions into a 'up' and a 'down' completion, but that only solves a part of the problem. The current failure handling does an automated rollback, so if UP fails somewhere the AP rolls back, which means it invokes the down callbacks. DOWN the other way round. We can solve that by changing the way how rollback is handled so it does not automatically roll back. if (callback() < 0) { store_state(); complete(UP); wait_for_being_kicked_again() } and on the control side have wait_for_completion(UP); if (UP->failed) { kick(DOWN); wait_for_completion(DOWN); } It's not entirely trivial, but I haven't seen a real problem with it yet. Thanks, tglx