From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v3 2/3] mutex: add support for wound/wait style locks, v3 Date: Mon, 27 May 2013 12:24:57 +0200 Message-ID: <20130527102457.GA4341@laptop> References: <20130428165914.17075.57751.stgit@patser> <20130428170407.17075.80082.stgit@patser> <20130430191422.GA5763@phenom.ffwll.local> <519CA976.9000109@canonical.com> <20130522161831.GQ18810@twins.programming.kicks-ass.net> <519CFF56.90600@canonical.com> <20130527082149.GE2781@laptop> <51A32F0E.9000206@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from merlin.infradead.org ([205.233.59.134]:39848 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757380Ab3E0KZ3 (ORCPT ); Mon, 27 May 2013 06:25:29 -0400 Content-Disposition: inline In-Reply-To: <51A32F0E.9000206@canonical.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Maarten Lankhorst Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, robclark@gmail.com, rostedt@goodmis.org, tglx@linutronix.de, mingo@elte.hu, linux-media@vger.kernel.org, Dave Airlie On Mon, May 27, 2013 at 12:01:50PM +0200, Maarten Lankhorst wrote: > > Again, early.. monday.. would a trylock, even if successful still need > > the ctx? > No ctx for trylock is supported. You can still do a trylock while > holding a context, but the mutex won't be a part of the context. > Normal lockdep rules apply. lib/locking-selftest.c: > > context + ww_mutex_lock first, then a trylock: > dotest(ww_test_context_try, SUCCESS, LOCKTYPE_WW); > > trylock first, then context + ww_mutex_lock: > dotest(ww_test_try_context, FAILURE, LOCKTYPE_WW); > > For now I don't want to add support for a trylock with context, I'm > very glad I managed to fix ttm locking to not require this any more, > and it was needed there only because it was a workaround for the > locking being wrong. There was no annotation for the buffer locking > it was using, so the real problem wasn't easy to spot. Ah, ok. My question really was whether there even was sense for a trylock with context. I couldn't come up with a case for it; but I think I see one now. The thing is; if there could exist something like: ww_mutex_trylock(struct ww_mutex *, struct ww_acquire_ctx *ctx); Then we should not now take away that name and make it mean something else; namely: ww_mutex_trylock_single(). Unless we want to allow .ctx=NULL to mean _single. As to why I proposed that (.ctx=NULL meaning _single); I suppose because I'm a minimalist at heart.