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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 D2777C433E1 for ; Mon, 8 Jun 2020 07:21:53 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 B2F9E204EF for ; Mon, 8 Jun 2020 07:21:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2F9E204EF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A4AC06E48C; Mon, 8 Jun 2020 07:21:33 +0000 (UTC) Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1C16089C59; Mon, 8 Jun 2020 00:58:11 +0000 (UTC) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1ji66y-0000nK-57; Mon, 08 Jun 2020 02:58:00 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Subject: [PATCH v2 06/18] dma-buf: Use sequence counter with associated wound/wait mutex Date: Mon, 8 Jun 2020 02:57:17 +0200 Message-Id: <20200608005729.1874024-7-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200608005729.1874024-1-a.darwish@linutronix.de> References: <20200519214547.352050-1-a.darwish@linutronix.de> <20200608005729.1874024-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1, SHORTCIRCUIT=-0.0001 X-Mailman-Approved-At: Mon, 08 Jun 2020 07:21:26 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: amd-gfx@lists.freedesktop.org, "Paul E. McKenney" , David Airlie , "Sebastian A. Siewior" , LKML , Steven Rostedt , =?UTF-8?q?Christian=20K=C3=B6nig?= , dri-devel@lists.freedesktop.org, "Ahmed S. Darwish" , Alex Deucher , Felix Kuehling , Thomas Gleixner Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" A sequence counter write side critical section must be protected by some form of locking to serialize writers. If the serialization primitive is not disabling preemption implicitly, preemption has to be explicitly disabled before entering the sequence counter write side critical section. The dma-buf reservation subsystem uses plain sequence counters to manage updates to reservations. Writer serialization is accomplished through a wound/wait mutex. Acquiring a wound/wait mutex does not disable preemption, so this needs to be done manually before and after the write side critical section. Use the newly-added seqcount_ww_mutex_t instead: - It associates the ww_mutex with the sequence count, which enables lockdep to validate that the write side critical section is properly serialized. - It removes the need to explicitly add preempt_disable/enable() around the write side critical section because the write_begin/end() functions for this new data type automatically do this. If lockdep is disabled this ww_mutex lock association is compiled out and has neither storage size nor runtime overhead. Signed-off-by: Ahmed S. Darwish --- drivers/dma-buf/dma-resv.c | 8 +------- drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 -- include/linux/dma-resv.h | 2 +- 3 files changed, 2 insertions(+), 10 deletions(-) diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 590ce7ad60a0..3aba2b2bfc48 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -128,7 +128,7 @@ subsys_initcall(dma_resv_lockdep); void dma_resv_init(struct dma_resv *obj) { ww_mutex_init(&obj->lock, &reservation_ww_class); - seqcount_init(&obj->seq); + seqcount_ww_mutex_init(&obj->seq, &obj->lock); RCU_INIT_POINTER(obj->fence, NULL); RCU_INIT_POINTER(obj->fence_excl, NULL); @@ -259,7 +259,6 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence) fobj = dma_resv_get_list(obj); count = fobj->shared_count; - preempt_disable(); write_seqcount_begin(&obj->seq); for (i = 0; i < count; ++i) { @@ -281,7 +280,6 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence) smp_store_mb(fobj->shared_count, count); write_seqcount_end(&obj->seq); - preempt_enable(); dma_fence_put(old); } EXPORT_SYMBOL(dma_resv_add_shared_fence); @@ -308,14 +306,12 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence) if (fence) dma_fence_get(fence); - preempt_disable(); write_seqcount_begin(&obj->seq); /* write_seqcount_begin provides the necessary memory barrier */ RCU_INIT_POINTER(obj->fence_excl, fence); if (old) old->shared_count = 0; write_seqcount_end(&obj->seq); - preempt_enable(); /* inplace update, no shared fences */ while (i--) @@ -393,13 +389,11 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) src_list = dma_resv_get_list(dst); old = dma_resv_get_excl(dst); - preempt_disable(); write_seqcount_begin(&dst->seq); /* write_seqcount_begin provides the necessary memory barrier */ RCU_INIT_POINTER(dst->fence_excl, new); RCU_INIT_POINTER(dst->fence, dst_list); write_seqcount_end(&dst->seq); - preempt_enable(); dma_resv_list_free(src_list); dma_fence_put(old); diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c index 6a5b91d23fd9..c71c0bb6ce26 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c @@ -258,11 +258,9 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo, new->shared_count = k; /* Install the new fence list, seqcount provides the barriers */ - preempt_disable(); write_seqcount_begin(&resv->seq); RCU_INIT_POINTER(resv->fence, new); write_seqcount_end(&resv->seq); - preempt_enable(); /* Drop the references to the removed fences or move them to ef_list */ for (i = j, k = 0; i < old->shared_count; ++i) { diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index a6538ae7d93f..d44a77e8a7e3 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -69,7 +69,7 @@ struct dma_resv_list { */ struct dma_resv { struct ww_mutex lock; - seqcount_t seq; + seqcount_ww_mutex_t seq; struct dma_fence __rcu *fence_excl; struct dma_resv_list __rcu *fence; -- 2.20.1 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel