From patchwork Tue May 12 08:59:29 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Daniel Vetter X-Patchwork-Id: 11542661 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 83A41139F for ; Tue, 12 May 2020 09:03:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66AB72186A for ; Tue, 12 May 2020 09:03:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="G3K7uswl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729348AbgELJAD (ORCPT ); Tue, 12 May 2020 05:00:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1729322AbgELJAB (ORCPT ); Tue, 12 May 2020 05:00:01 -0400 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA361C05BD09 for ; Tue, 12 May 2020 01:59:59 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id m24so11242153wml.2 for ; Tue, 12 May 2020 01:59:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=I6zGk0sRXoiLMVlOrHdYKmGYdqgb8HIUHeWjfHU8LZ8=; b=G3K7uswlmhW+rpia5CreMV57ZkKdKlwZ6FOlSyfm3Oe7LuGmiEiRHD/PML6gjh4GhM OdvDdQt4u51YIl+RwDLbW7P8kjQMLKpQZcHKzE4dlQdQnOJqX7Su2t5BwmDsqLUnYibz JMBsPiQPy7q4aI4KfXGjLvCIMnBefB60TFyyI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=I6zGk0sRXoiLMVlOrHdYKmGYdqgb8HIUHeWjfHU8LZ8=; b=FXEMqVI0w+69WYMKPsvDSvIninlHn92vWdokY4yHiU199BQo9bF/5+xanQOJr7U/mg My5ZJ+wmoXvhyyHr7BGrQScRAOgIcoZJuNs4wtSILfFBhs3hOSRXot4iA/3gdh93mquN N2HZ4sgN8/vHGl7T7K4XRvSV4kQg3AUWz/J8wSZYELHJs1NoDZpa3FRG3G7MsUMlXstX FlE3EidhKIIiOVXTlOfCTMX29rKwlkitEWYH/o3e6G3Phdn5+rOG5d/gmwjbPfracEBi QXAUIKxOg2iqgW1nfy3zUDItunK3Y1pB4NqScXcVLbWyt/M46H6AvCcyjGP5JNaPBPwV UZoQ== X-Gm-Message-State: AGi0PuZc1dNMQYsuntnI+saGWazxua3RqDsWFhkaXYRn4PPjYQdQzmoa dSGS395n/RFNlBW3sM6Z4RmY1xjdKB8= X-Google-Smtp-Source: APiQypLCYf7Wgh0Wtz0pUmQn/xpulX/EPJ0KyLgnUHWq+1CmCns3LkuSYY1ZCdFMCm+vHgIBfsEl0Q== X-Received: by 2002:a1c:3bc5:: with SMTP id i188mr25545127wma.90.1589273998427; Tue, 12 May 2020 01:59:58 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id y10sm18845457wrd.95.2020.05.12.01.59.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 May 2020 01:59:57 -0700 (PDT) From: Daniel Vetter To: DRI Development Cc: LKML , Daniel Vetter , linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, Chris Wilson , Maarten Lankhorst , =?utf-8?q?Christian_?= =?utf-8?q?K=C3=B6nig?= , Daniel Vetter Subject: [RFC 02/17] dma-fence: basic lockdep annotations Date: Tue, 12 May 2020 10:59:29 +0200 Message-Id: <20200512085944.222637-3-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200512085944.222637-1-daniel.vetter@ffwll.ch> References: <20200512085944.222637-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org 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 Reviewed-by: Maarten Lankhorst Reviewed-by: Thomas Hellstrom --- drivers/dma-buf/dma-fence.c | 53 +++++++++++++++++++++++++++++++++++++ include/linux/dma-fence.h | 12 +++++++++ 2 files changed, 65 insertions(+) diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 6802125349fb..d5c0fd2efc70 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -110,6 +110,52 @@ u64 dma_fence_context_alloc(unsigned num) } EXPORT_SYMBOL(dma_fence_context_alloc); +#ifdef CONFIG_LOCKDEP +struct lockdep_map dma_fence_lockdep_map = { + .name = "dma_fence_map" +}; + +bool dma_fence_begin_signalling(void) +{ + /* explicitly nesting ... */ + if (lock_is_held_type(&dma_fence_lockdep_map, 1)) + return true; + + /* rely on might_sleep check for soft/hardirq locks */ + if (in_atomic()) + return true; + + /* ... and non-recursive readlock */ + lock_acquire(&dma_fence_lockdep_map, 0, 0, 1, 1, NULL, _RET_IP_); + + return false; +} +EXPORT_SYMBOL(dma_fence_begin_signalling); + +void dma_fence_end_signalling(bool cookie) +{ + if (cookie) + return; + + lock_release(&dma_fence_lockdep_map, _RET_IP_); +} +EXPORT_SYMBOL(dma_fence_end_signalling); + +void __dma_fence_might_wait(void) +{ + bool tmp; + + tmp = lock_is_held_type(&dma_fence_lockdep_map, 1); + if (tmp) + lock_release(&dma_fence_lockdep_map, _THIS_IP_); + lock_map_acquire(&dma_fence_lockdep_map); + lock_map_release(&dma_fence_lockdep_map); + if (tmp) + lock_acquire(&dma_fence_lockdep_map, 0, 0, 1, 1, NULL, _THIS_IP_); +} +#endif + + /** * dma_fence_signal_locked - signal completion of a fence * @fence: the fence to signal @@ -170,14 +216,19 @@ int dma_fence_signal(struct dma_fence *fence) { unsigned long flags; int ret; + bool tmp; if (!fence) return -EINVAL; + tmp = dma_fence_begin_signalling(); + spin_lock_irqsave(fence->lock, flags); ret = dma_fence_signal_locked(fence); spin_unlock_irqrestore(fence->lock, flags); + dma_fence_end_signalling(tmp); + return ret; } EXPORT_SYMBOL(dma_fence_signal); @@ -211,6 +262,8 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout) if (timeout > 0) might_sleep(); + __dma_fence_might_wait(); + trace_dma_fence_wait_start(fence); if (fence->ops->wait) ret = fence->ops->wait(fence, intr, timeout); diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 3347c54f3a87..3f288f7db2ef 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -357,6 +357,18 @@ dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep) } while (1); } +#ifdef CONFIG_LOCKDEP +bool dma_fence_begin_signalling(void); +void dma_fence_end_signalling(bool cookie); +#else +static inline bool dma_fence_begin_signalling(void) +{ + return true; +} +static inline void dma_fence_end_signalling(bool cookie) {} +static inline void __dma_fence_might_wait(void) {} +#endif + int dma_fence_signal(struct dma_fence *fence); int dma_fence_signal_locked(struct dma_fence *fence); signed long dma_fence_default_wait(struct dma_fence *fence,