From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu Date: Tue, 20 Feb 2018 14:22:54 +0100 Message-ID: <20180220132254.GB25201@hirez.programming.kicks-ass.net> References: <20180215141944.4332-1-christian.koenig@amd.com> <20180220123532.GD25314@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org List-Id: amd-gfx.lists.freedesktop.org T24gVHVlLCBGZWIgMjAsIDIwMTggYXQgMDI6MDg6MjZQTSArMDEwMCwgQ2hyaXN0aWFuIEvDtm5p ZyB3cm90ZToKPiBBbSAyMC4wMi4yMDE4IHVtIDEzOjM1IHNjaHJpZWIgUGV0ZXIgWmlqbHN0cmE6 Cj4gPiA+ICtzdGF0aWMgaW5saW5lIGJvb2wgd3dfbXV0ZXhfaXNfb3duZWRfYnkoc3RydWN0IHd3 X211dGV4ICpsb2NrLAo+ID4gPiArCQkJCQlzdHJ1Y3QgdGFza19zdHJ1Y3QgKnRhc2ssCj4gPiA+ ICsJCQkJCXN0cnVjdCB3d19hY3F1aXJlX2N0eCAqY3R4KQo+ID4gPiArewo+ID4gPiArCXJldHVy biBsaWtlbHkoX19tdXRleF9vd25lcigmbG9jay0+YmFzZSkgPT0gdGFzaykgJiYKPiA+ID4gKwkJ UkVBRF9PTkNFKGxvY2stPmN0eCkgPT0gY3R4Owo+ID4gPiArfQo+ID4gTmFrIG9uIHRoYXQgaW50 ZXJmYWNlLCB0aGF0J3MgcmFjeSBhbmQgYnJva2VuIGJ5IGRlc2lnbi4KPiAKPiBXaHk/CgpJZiB0 YXNrICE9IGN1cnJlbnQgeW91IGNhbiByYWNlIHdpdGggYSBjb25jdXJyZW50IG11dGV4X3VubG9j aygpLgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpkcmkt ZGV2ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5vcmcKaHR0cHM6 Ly9saXN0cy5mcmVlZGVza3RvcC5vcmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2ZWwK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751903AbeBTNXC (ORCPT ); Tue, 20 Feb 2018 08:23:02 -0500 Received: from merlin.infradead.org ([205.233.59.134]:55774 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751718AbeBTNXA (ORCPT ); Tue, 20 Feb 2018 08:23:00 -0500 Date: Tue, 20 Feb 2018 14:22:54 +0100 From: Peter Zijlstra To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu Message-ID: <20180220132254.GB25201@hirez.programming.kicks-ass.net> References: <20180215141944.4332-1-christian.koenig@amd.com> <20180220123532.GD25314@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 02:08:26PM +0100, Christian König wrote: > Am 20.02.2018 um 13:35 schrieb Peter Zijlstra: > > > +static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock, > > > + struct task_struct *task, > > > + struct ww_acquire_ctx *ctx) > > > +{ > > > + return likely(__mutex_owner(&lock->base) == task) && > > > + READ_ONCE(lock->ctx) == ctx; > > > +} > > Nak on that interface, that's racy and broken by design. > > Why? If task != current you can race with a concurrent mutex_unlock().