From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752517AbeBTPWK (ORCPT ); Tue, 20 Feb 2018 10:22:10 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:50576 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752339AbeBTPWG (ORCPT ); Tue, 20 Feb 2018 10:22:06 -0500 Date: Tue, 20 Feb 2018 16:21:58 +0100 From: Peter Zijlstra To: christian.koenig@amd.com Cc: dev@mblankhorst.nl, dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/4] locking/ww_mutex: add ww_mutex_is_owned_by function v3 Message-ID: <20180220152158.GH25201@hirez.programming.kicks-ass.net> References: <20180220125829.27060-1-christian.koenig@amd.com> <20180220131253.GF25314@hirez.programming.kicks-ass.net> <8fd80334-4d0e-8ed0-8a09-02a7e36a0eae@gmail.com> <20180220135709.GD25201@hirez.programming.kicks-ass.net> <20180220145413.GF25201@hirez.programming.kicks-ass.net> <2dac8ec9-c54a-7dd1-af4e-62f2bc1a959c@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2dac8ec9-c54a-7dd1-af4e-62f2bc1a959c@gmail.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 20, 2018 at 04:05:49PM +0100, Christian König wrote: > Am 20.02.2018 um 15:54 schrieb Peter Zijlstra: > > On Tue, Feb 20, 2018 at 03:34:07PM +0100, Christian König wrote: > > > > OK, but neither case would in fact need the !ctx case right? That's just > > > > there for completeness sake? > > > Unfortunately not. TTM uses trylock to lock BOs which are about to be > > > evicted to make room for all the BOs locked with a ctx. > > > > > > I need to be able to distinct between the BOs which are trylocked and those > > > which are locked with a ctx. > > > > > > Writing this I actually noticed the current version is buggy, cause even > > > when we check the mutex owner we still need to make sure that the ctx in the > > > lock is NULL. > > Hurm... I can't remember why trylocks behave like that, and it seems > > rather unfortunate / inconsistent. > > Actually for me that is rather fortunate, cause I need to distinct between > the locks acquired through trylock and lock. I suppose that would always be possible using: ww_mutex_trylock(.ctx=NULL), and it could be that there simply weren't any immediate uses for a !NULL trylock and it was thus not implemented. But that is all very long ago..