From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [patch V2 18/29] lockdep: Move stack trace logic into check_prev_add() Date: Wed, 24 Apr 2019 21:45:05 +0200 Message-ID: <20190424194505.GR11158@hirez.programming.kicks-ass.net> References: <20190418084119.056416939@linutronix.de> <20190418084254.729689921@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20190418084254.729689921@linutronix.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Thomas Gleixner Cc: Mike Snitzer , David Airlie , Catalin Marinas , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, dm-devel@redhat.com, Alexander Potapenko , Christoph Lameter , Christoph Hellwig , Alasdair Kergon , Marek Szyprowski , linux-arch@vger.kernel.org, x86@kernel.org, kasan-dev@googlegroups.com, David Rientjes , Andrey Ryabinin , Alexey Dobriyan , intel-gfx@lists.freedesktop.org, Johannes Thumshirn , Akinobu Mita , Steven Rostedt , Josef Bacik , Rodrigo Vivi , Mike Rapoport , Andy Lutomirski , Josh Poimboeuf List-Id: linux-arch.vger.kernel.org T24gVGh1LCBBcHIgMTgsIDIwMTkgYXQgMTA6NDE6MzdBTSArMDIwMCwgVGhvbWFzIEdsZWl4bmVy IHdyb3RlOgo+IFRoZXJlIGlzIG9ubHkgb25lIGNhbGxlciBvZiBjaGVja19wcmV2X2FkZCgpIHdo aWNoIGhhbmRzIGluIGEgemVyb2VkIHN0cnVjdAo+IHN0YWNrIHRyYWNlIGFuZCBhIGZ1bmN0aW9u IHBvaW50ZXIgdG8gc2F2ZV9zdGFjaygpLiBJbnNpZGUgY2hlY2tfcHJldl9hZGQoKQo+IHRoZSBz dGFja190cmFjZSBzdHJ1Y3QgaXMgY2hlY2tlZCBmb3IgYmVpbmcgZW1wdHksIHdoaWNoIGlzIGFs d2F5cwo+IHRydWUuIEJhc2VkIG9uIHRoYXQgb25lIGNvZGUgcGF0aCBzdG9yZXMgYSBzdGFjayB0 cmFjZSB3aGljaCBpcyB1bnVzZWQuIFRoZQo+IGNvbW1lbnQgdGhlcmUgZG9lcyBub3QgbWFrZSBz ZW5zZSBlaXRoZXIuIEl0J3MgYWxsIGxlZnRvdmVycyBmcm9tCj4gaGlzdG9yaWNhbCBsb2NrZGVw IGNvZGUgKGNyb3NzIHJlbGVhc2UpLgoKSSB3YXMgbW9yZSBvciBsZXNzIGV4cGVjdGluZyBhIHJl dmVydCBvZjoKCmNlMDdhOTQxNWYyNiAoImxvY2tpbmcvbG9ja2RlcDogTWFrZSBjaGVja19wcmV2 X2FkZCgpIGFibGUgdG8gaGFuZGxlIGV4dGVybmFsIHN0YWNrX3RyYWNlIikKCkFuZCB0aGVuIEkg cmVhZCB0aGUgY29tbWVudCB0aGF0IHdlbnQgd2l0aCB0aGUgInN0YXRpYyBzdHJ1Y3QKc3RhY2tf dHJhY2UgdHJhY2UiIHRoYXQgZ290IHJlbW92ZWQgKGluIHRoZSBhYm92ZSBjb21taXQpIGFuZCBy ZWFsaXplZAp0aGF0IHlvdXIgcGF0Y2ggd2lsbCBjb25zdW1lIG1vcmUgc3RhY2sgZW50cmllcy4K ClRoZSBwcm9ibGVtIGlzIHdoZW4gdGhlIGhlbGQgbG9jayBzdGFjayBpbiBjaGVja19wcmV2c19h ZGQoKSBoYXMgbXVsdHBsZQp0cnlsb2NrIGVudHJpZXMgb24gdG9wLCBpbiB0aGF0IGNhc2Ugd2Ug Y2FsbCBjaGVja19wcmV2X2FkZCgpIG11bHRpcGxlCnRpbWVzLCBhbmQgdGhpcyBwYXRjaCB3aWxs IHRoZW4gc2F2ZSB0aGUgZXhhY3Qgc2FtZSBzdGFjay10cmFjZSBtdWx0aXBsZQp0aW1lcywgY29u c3VtaW5nIHN0YXRpYyByZXNvdXJjZXMuCgpQb3NzaWJseSB3ZSBzaG91bGQgY29weSB3aGF0IHN0 YWNrZGVwb3QgZG9lcyAoYnV0IHdlIGNhbm5vdCB1c2UgaXQKZGlyZWN0bHkgYmVjYXVzZSBzdGFj a2RlcG90IHVzZXMgbG9ja3M7IGJ1dCBwb3NzaWJsZSB3ZSBjYW4gc2hhcmUgYml0cyksCmJ1dCB0 aGF0IGlzIGEgcGF0Y2ggZm9yIGFub3RoZXIgZGF5IEkgdGhpbmsuCgpTbyB3aGlsZSBjb252b2x1 dGVkLCBwZXJoYXBzIHdlIHNob3VsZCByZXRhaW4gdGhpcyBjb2RlIGZvciBub3cuCl9fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmRyaS1kZXZlbCBtYWlsaW5n IGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpodHRwczovL2xpc3RzLmZyZWVk ZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1kZXZlbA== From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:60860 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726157AbfDXTph (ORCPT ); Wed, 24 Apr 2019 15:45:37 -0400 Date: Wed, 24 Apr 2019 21:45:05 +0200 From: Peter Zijlstra Subject: Re: [patch V2 18/29] lockdep: Move stack trace logic into check_prev_add() Message-ID: <20190424194505.GR11158@hirez.programming.kicks-ass.net> References: <20190418084119.056416939@linutronix.de> <20190418084254.729689921@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190418084254.729689921@linutronix.de> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Thomas Gleixner Cc: LKML , Josh Poimboeuf , x86@kernel.org, Andy Lutomirski , Steven Rostedt , Alexander Potapenko , Alexey Dobriyan , Andrew Morton , Pekka Enberg , linux-mm@kvack.org, David Rientjes , Christoph Lameter , Catalin Marinas , Dmitry Vyukov , Andrey Ryabinin , kasan-dev@googlegroups.com, Mike Rapoport , Akinobu Mita , iommu@lists.linux-foundation.org, Robin Murphy , Christoph Hellwig , Marek Szyprowski , Johannes Thumshirn , David Sterba , Chris Mason , Josef Bacik , linux-btrfs@vger.kernel.org, dm-devel@redhat.com, Mike Snitzer , Alasdair Kergon , intel-gfx@lists.freedesktop.org, Joonas Lahtinen , Maarten Lankhorst , dri-devel@lists.freedesktop.org, David Airlie , Jani Nikula , Daniel Vetter , Rodrigo Vivi , linux-arch@vger.kernel.org Message-ID: <20190424194505._4rY7n8LnKeND5iZgXWoPXvnQRM86F7sIVI4Bn1RrCk@z> On Thu, Apr 18, 2019 at 10:41:37AM +0200, Thomas Gleixner wrote: > There is only one caller of check_prev_add() which hands in a zeroed struct > stack trace and a function pointer to save_stack(). Inside check_prev_add() > the stack_trace struct is checked for being empty, which is always > true. Based on that one code path stores a stack trace which is unused. The > comment there does not make sense either. It's all leftovers from > historical lockdep code (cross release). I was more or less expecting a revert of: ce07a9415f26 ("locking/lockdep: Make check_prev_add() able to handle external stack_trace") And then I read the comment that went with the "static struct stack_trace trace" that got removed (in the above commit) and realized that your patch will consume more stack entries. The problem is when the held lock stack in check_prevs_add() has multple trylock entries on top, in that case we call check_prev_add() multiple times, and this patch will then save the exact same stack-trace multiple times, consuming static resources. Possibly we should copy what stackdepot does (but we cannot use it directly because stackdepot uses locks; but possible we can share bits), but that is a patch for another day I think. So while convoluted, perhaps we should retain this code for now.