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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 6C2F5C433E1 for ; Thu, 28 May 2020 13:43:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 467B220814 for ; Thu, 28 May 2020 13:43:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=shipmail.org header.i=@shipmail.org header.b="i8189QXo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390521AbgE1Nni (ORCPT ); Thu, 28 May 2020 09:43:38 -0400 Received: from pio-pvt-msa3.bahnhof.se ([79.136.2.42]:33920 "EHLO pio-pvt-msa3.bahnhof.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390468AbgE1Nng (ORCPT ); Thu, 28 May 2020 09:43:36 -0400 X-Greylist: delayed 352 seconds by postgrey-1.27 at vger.kernel.org; Thu, 28 May 2020 09:43:35 EDT Received: from localhost (localhost [127.0.0.1]) by pio-pvt-msa3.bahnhof.se (Postfix) with ESMTP id D92C53F3E6; Thu, 28 May 2020 15:37:40 +0200 (CEST) Authentication-Results: pio-pvt-msa3.bahnhof.se; dkim=pass (1024-bit key; unprotected) header.d=shipmail.org header.i=@shipmail.org header.b=i8189QXo; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at bahnhof.se Received: from pio-pvt-msa3.bahnhof.se ([127.0.0.1]) by localhost (pio-pvt-msa3.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tWEVle6VlQ0m; Thu, 28 May 2020 15:37:36 +0200 (CEST) Received: from mail1.shipmail.org (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) (Authenticated sender: mb878879) by pio-pvt-msa3.bahnhof.se (Postfix) with ESMTPA id 4772F3F398; Thu, 28 May 2020 15:37:33 +0200 (CEST) Received: from Gunillas-MacBook-Pro.local (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) by mail1.shipmail.org (Postfix) with ESMTPSA id 5B030360165; Thu, 28 May 2020 15:37:33 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=shipmail.org; s=mail; t=1590673053; bh=hzBvGtdMVY1yFDhX6vHBpO0alm4n63ua22McT7gZosc=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=i8189QXoVaRwcn+moTSIMQD7TJ7H9n0I1yFj2IMYL7PullzNred3UO8BAAnz2DeMq j/VrfOha1hYBt/0oje3SsVmDflH1Wva31htryiedFwwGczZJYD1NmbCNmJNQfVSK5z 6PWj3YdF/MSpTB+pJ0H/4RhVF8RvgNw2PZv4Ful4= Subject: Re: [RFC 02/17] dma-fence: basic lockdep annotations To: Daniel Vetter , DRI Development Cc: linux-rdma@vger.kernel.org, intel-gfx@lists.freedesktop.org, LKML , amd-gfx@lists.freedesktop.org, Chris Wilson , linaro-mm-sig@lists.linaro.org, Daniel Vetter , =?UTF-8?Q?Christian_K=c3=b6nig?= , linux-media@vger.kernel.org References: <20200512085944.222637-1-daniel.vetter@ffwll.ch> <20200512085944.222637-3-daniel.vetter@ffwll.ch> From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= Message-ID: <81b3a3be-b818-9e7c-e93e-ecf161bec94c@shipmail.org> Date: Thu, 28 May 2020 15:36:56 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: <20200512085944.222637-3-daniel.vetter@ffwll.ch> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-12 10:59, Daniel Vetter wrote: > Design is similar to the lockdep annotations for workers, but with > some twists: > > - We use a read-lock for the execution/worker/completion side, so that > this explicit annotation can be more liberally sprinkled around. > With read locks lockdep isn't going to complain if the read-side > isn't nested the same way under all circumstances, so ABBA deadlocks > are ok. Which they are, since this is an annotation only. > > - We're using non-recursive lockdep read lock mode, since in recursive > read lock mode lockdep does not catch read side hazards. And we > _very_ much want read side hazards to be caught. For full details of > this limitation see > > commit e91498589746065e3ae95d9a00b068e525eec34f > Author: Peter Zijlstra > Date: Wed Aug 23 13:13:11 2017 +0200 > > locking/lockdep/selftests: Add mixed read-write ABBA tests > > - To allow nesting of the read-side explicit annotations we explicitly > keep track of the nesting. lock_is_held() allows us to do that. > > - The wait-side annotation is a write lock, and entirely done within > dma_fence_wait() for everyone by default. > > - To be able to freely annotate helper functions I want to make it ok > to call dma_fence_begin/end_signalling from soft/hardirq context. > First attempt was using the hardirq locking context for the write > side in lockdep, but this forces all normal spinlocks nested within > dma_fence_begin/end_signalling to be spinlocks. That bollocks. > > The approach now is to simple check in_atomic(), and for these cases > entirely rely on the might_sleep() check in dma_fence_wait(). That > will catch any wrong nesting against spinlocks from soft/hardirq > contexts. > > The idea here is that every code path that's critical for eventually > signalling a dma_fence should be annotated with > dma_fence_begin/end_signalling. The annotation ideally starts right > after a dma_fence is published (added to a dma_resv, exposed as a > sync_file fd, attached to a drm_syncobj fd, or anything else that > makes the dma_fence visible to other kernel threads), up to and > including the dma_fence_wait(). Examples are irq handlers, the > scheduler rt threads, the tail of execbuf (after the corresponding > fences are visible), any workers that end up signalling dma_fences and > really anything else. Not annotated should be code paths that only > complete fences opportunistically as the gpu progresses, like e.g. > shrinker/eviction code. > > The main class of deadlocks this is supposed to catch are: > > Thread A: > > mutex_lock(A); > mutex_unlock(A); > > dma_fence_signal(); > > Thread B: > > mutex_lock(A); > dma_fence_wait(); > mutex_unlock(A); > > Thread B is blocked on A signalling the fence, but A never gets around > to that because it cannot acquire the lock A. > > Note that dma_fence_wait() is allowed to be nested within > dma_fence_begin/end_signalling sections. To allow this to happen the > read lock needs to be upgraded to a write lock, which means that any > other lock is acquired between the dma_fence_begin_signalling() call and > the call to dma_fence_wait(), and still held, this will result in an > immediate lockdep complaint. The only other option would be to not > annotate such calls, defeating the point. Therefore these annotations > cannot be sprinkled over the code entirely mindless to avoid false > positives. > > v2: handle soft/hardirq ctx better against write side and dont forget > EXPORT_SYMBOL, drivers can't use this otherwise. > > Cc: linux-media@vger.kernel.org > Cc: linaro-mm-sig@lists.linaro.org > Cc: linux-rdma@vger.kernel.org > Cc: amd-gfx@lists.freedesktop.org > Cc: intel-gfx@lists.freedesktop.org > Cc: Chris Wilson > Cc: Maarten Lankhorst > Cc: Christian König > Signed-off-by: Daniel Vetter LGTM. Perhaps some in-code documentation on how to use the new functions are called. Otherwise for patch 2 and 3, Reviewed-by: Thomas Hellstrom