From patchwork Sat Apr 20 21:32:13 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Ma=C3=ADra_Canal?= X-Patchwork-Id: 13637219 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 393DEC07C79 for ; Sat, 20 Apr 2024 21:38:05 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 0B0D110EAEC; Sat, 20 Apr 2024 21:38:04 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=igalia.com header.i=@igalia.com header.b="mgazUr2r"; dkim-atps=neutral Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by gabe.freedesktop.org (Postfix) with ESMTPS id 22CEC10EAEC for ; Sat, 20 Apr 2024 21:38:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To: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=RwDW9z/sV4fNpTMXX0otvLZPx8ADWt1ubYSgRO0MqoM=; b=mgazUr2rItfEz33mOBfBpNqGEr p+b6JNWfh3e0onOgwcUlB+gcEvC43K3UFFpNteZDU74UcuC4c/ZDHMYrYkYFZsbE7dWCziHUArSbo oL4jjTnu/w6tuoKSMln6GXzhC8TNbCY5EZDAKRwN/3ciaFZZeA7BFaRTW2+oKzJGPMj+a9eUaYUNx kZlNXB7WAU60ZKIQN5nYhKdZ+Zoij7DdkAlVxLDY5HCwoVbsCIK0LjigFqv/ST2GipK7fVAY+ubQB EvuLNtvSDtvWG5E2wVbC7Ni4tRnhS9pQMejIYDLu4qeQyKRtj/wDRG9YPQPC511eq5Xy4UfGX8V2b wVdPGwIg==; Received: from [179.234.232.152] (helo=morissey..) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1ryIPC-006j7P-0d; Sat, 20 Apr 2024 23:37:54 +0200 From: =?utf-8?q?Ma=C3=ADra_Canal?= To: Melissa Wen , Chema Casanova , Tvrtko Ursulin , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter Cc: dri-devel@lists.freedesktop.org, kernel-dev@igalia.com, =?utf-8?q?Ma?= =?utf-8?q?=C3=ADra_Canal?= , Tvrtko Ursulin Subject: [PATCH v3 5/5] drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler Date: Sat, 20 Apr 2024 18:32:13 -0300 Message-ID: <20240420213632.339941-7-mcanal@igalia.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240420213632.339941-2-mcanal@igalia.com> References: <20240420213632.339941-2-mcanal@igalia.com> MIME-Version: 1.0 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: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" In V3D, the conclusion of a job is indicated by a IRQ. When a job finishes, then we update the local and the global GPU stats of that queue. But, while the GPU stats are being updated, a user might be reading the stats from sysfs or fdinfo. For example, on `gpu_stats_show()`, we could think about a scenario where `v3d->queue[queue].start_ns != 0`, then an interrupt happens, we update the value of `v3d->queue[queue].start_ns` to 0, we come back to `gpu_stats_show()` to calculate `active_runtime` and now, `active_runtime = timestamp`. In this simple example, the user would see a spike in the queue usage, that didn't match reality. In order to address this issue properly, use a seqcount to protect read and write sections of the code. Fixes: 09a93cc4f7d1 ("drm/v3d: Implement show_fdinfo() callback for GPU usage stats") Reported-by: Tvrtko Ursulin Signed-off-by: Maíra Canal Reviewed-by: Tvrtko Ursulin --- drivers/gpu/drm/v3d/v3d_drv.c | 14 ++++++++++---- drivers/gpu/drm/v3d/v3d_drv.h | 7 +++++++ drivers/gpu/drm/v3d/v3d_gem.c | 1 + drivers/gpu/drm/v3d/v3d_sched.c | 7 +++++++ 4 files changed, 25 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/v3d_drv.c index 2ec359ed2def..28b7ddce7747 100644 --- a/drivers/gpu/drm/v3d/v3d_drv.c +++ b/drivers/gpu/drm/v3d/v3d_drv.c @@ -121,6 +121,7 @@ v3d_open(struct drm_device *dev, struct drm_file *file) 1, NULL); memset(&v3d_priv->stats[i], 0, sizeof(v3d_priv->stats[i])); + seqcount_init(&v3d_priv->stats[i].lock); } v3d_perfmon_open_file(v3d_priv); @@ -145,10 +146,15 @@ v3d_postclose(struct drm_device *dev, struct drm_file *file) void v3d_get_stats(const struct v3d_stats *stats, u64 timestamp, u64 *active_runtime, u64 *jobs_completed) { - *active_runtime = stats->enabled_ns; - if (stats->start_ns) - *active_runtime += timestamp - stats->start_ns; - *jobs_completed = stats->jobs_completed; + unsigned int seq; + + do { + seq = read_seqcount_begin(&stats->lock); + *active_runtime = stats->enabled_ns; + if (stats->start_ns) + *active_runtime += timestamp - stats->start_ns; + *jobs_completed = stats->jobs_completed; + } while (read_seqcount_retry(&stats->lock, seq)); } static void v3d_show_fdinfo(struct drm_printer *p, struct drm_file *file) diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h index ff06dc1cc078..a2c516fe6d79 100644 --- a/drivers/gpu/drm/v3d/v3d_drv.h +++ b/drivers/gpu/drm/v3d/v3d_drv.h @@ -40,6 +40,13 @@ struct v3d_stats { u64 start_ns; u64 enabled_ns; u64 jobs_completed; + + /* + * This seqcount is used to protect the access to the GPU stats + * variables. It must be used as, while we are reading the stats, + * IRQs can happen and the stats can be updated. + */ + seqcount_t lock; }; struct v3d_queue_state { diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c index 0086081a9261..da8faf3b9011 100644 --- a/drivers/gpu/drm/v3d/v3d_gem.c +++ b/drivers/gpu/drm/v3d/v3d_gem.c @@ -251,6 +251,7 @@ v3d_gem_init(struct drm_device *dev) queue->fence_context = dma_fence_context_alloc(1); memset(&queue->stats, 0, sizeof(queue->stats)); + seqcount_init(&queue->stats.lock); } spin_lock_init(&v3d->mm_lock); diff --git a/drivers/gpu/drm/v3d/v3d_sched.c b/drivers/gpu/drm/v3d/v3d_sched.c index b9614944931c..7cd8c335cd9b 100644 --- a/drivers/gpu/drm/v3d/v3d_sched.c +++ b/drivers/gpu/drm/v3d/v3d_sched.c @@ -114,16 +114,23 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); + write_seqcount_begin(&local_stats->lock); local_stats->start_ns = now; + write_seqcount_end(&local_stats->lock); + + write_seqcount_begin(&global_stats->lock); global_stats->start_ns = now; + write_seqcount_end(&global_stats->lock); } static void v3d_stats_update(struct v3d_stats *stats, u64 now) { + write_seqcount_begin(&stats->lock); stats->enabled_ns += now - stats->start_ns; stats->jobs_completed++; stats->start_ns = 0; + write_seqcount_end(&stats->lock); } void