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: iommu@lists.linux-foundation.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: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C617FC282CE for ; Wed, 24 Apr 2019 19:45:27 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 96F8320652 for ; Wed, 24 Apr 2019 19:45:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jnXyb2lO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 96F8320652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 68F791634; Wed, 24 Apr 2019 19:45:27 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id B7A6C12AD for ; Wed, 24 Apr 2019 19:45:25 +0000 (UTC) X-Greylist: greylisting inactive for cl@linux.com in SQLgrey-1.7.6 X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 635D0870; Wed, 24 Apr 2019 19:45:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=nXNCzgXPp/MC/y/PJgs7pmMKbFnjx8a6N8WFYhwtNcs=; b=jnXyb2lOVttIJoTmHH09wDdgf n8NwsMb9Q8EZ9BhZYTUEmA/PHtyPiQZOmqBu9mXa6yS7FNimIsZTp3th5+3stcuYygHbNmLLYqBGT QahsATylTqjWyQwmQWDXx0qU89AA6/OXLd2NCoPGpUOZ+2qhJ4st3eHGbksMYs7v8Vz1EtlVHBU/V 0d2uWTvtE1ut2NEV0rW9PoEWWmPOPkZ6B4Ll/v8YqCWjQwzFWcsIDvwui3aaYqTf72W1WXM1j/0xM JpCvyP3P7MY/egBVMNbkcye19upsSYlZcw08/CLq5k4oepPII8zRfmSr6JNXtPbV5jb8VqzdiXZp7 XpWmu0naw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hJNpM-0005aH-OA; Wed, 24 Apr 2019 19:45:08 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E5F80203E8871; Wed, 24 Apr 2019 21:45:05 +0200 (CEST) Date: Wed, 24 Apr 2019 21:45:05 +0200 From: Peter Zijlstra To: Thomas Gleixner 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-Disposition: inline In-Reply-To: <20190418084254.729689921@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: Mike Snitzer , David Airlie , Catalin Marinas , Joonas Lahtinen , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, dm-devel@redhat.com, Alexander Potapenko , Christoph Lameter , Christoph Hellwig , Alasdair Kergon , 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 , Maarten Lankhorst , Akinobu Mita , Steven Rostedt , Josef Bacik , Rodrigo Vivi , Mike Rapoport , Jani Nikula , Andy Lutomirski , Josh Poimboeuf , David Sterba , Dmitry Vyukov , Chris Mason , LKML , Pekka Enberg , iommu@lists.linux-foundation.org, Daniel Vetter , Andrew Morton , Robin Murphy , linux-btrfs@vger.kernel.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org Message-ID: <20190424194505.AdRLxbEYEv14D2loFulbrE4oZYOezHKtELiBYlmfHko@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. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu