From patchwork Tue Aug 13 10:25:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Tvrtko Ursulin X-Patchwork-Id: 13761744 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 E3E1AC52D7B for ; Tue, 13 Aug 2024 10:25:14 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 1E58B10E2DD; Tue, 13 Aug 2024 10:25:14 +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="TNFHMYlH"; dkim-atps=neutral Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6ED2F10E2DE for ; Tue, 13 Aug 2024 10:25:10 +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=RQn5YfxTb0VAMLBpx3eWU99G17Q99Oq4xeBq3YqSESc=; b=TNFHMYlH1OE+ssroX6vcTKJyG7 V2dfIIHVVFZhe/miWjWhlAHpfo6IAvtjpsd1shbqQkwjI7wrLHzgxGwKbM5A3mAHnvxokx9pWOwdT G3T2r2IRsXhBhRei7fTB8NNAz8Ndt2vEfWt8qOBAFPqT9BJNNia5goIIL0EK32qwnQf+ZEnbTzu3j Z9lbl8vDwNYk0KkcIlXC9S9NURcCGbfY5kDQuy8ZZW6bgohBgXoJS513tfRdzxSNVLkVh1UCt6Ucq EgrsZx06UZhJGchkirXHd962S0nOheZ9mSQ1fMHLUtTJpDMxXKC8FuxGb65/gpqgfavTjlZhyLz7c 6MzScIoA==; Received: from [84.69.19.168] (helo=localhost) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1sdoiC-00Bsuw-Mu; Tue, 13 Aug 2024 12:25:08 +0200 From: Tvrtko Ursulin To: dri-devel@lists.freedesktop.org Cc: kernel-dev@igalia.com, Tvrtko Ursulin , =?utf-8?q?Ma=C3=ADra_Canal?= Subject: [PATCH 2/2] drm/v3d: Appease lockdep while updating GPU stats Date: Tue, 13 Aug 2024 11:25:05 +0100 Message-ID: <20240813102505.80512-2-tursulin@igalia.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240813102505.80512-1-tursulin@igalia.com> References: <20240813102505.80512-1-tursulin@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" From: Tvrtko Ursulin Lockdep thinks our seqcount_t usage is unsafe because the update path can be both from irq and worker context: [ ] ================================ [ ] WARNING: inconsistent lock state [ ] 6.10.3-v8-16k-numa #159 Tainted: G WC [ ] -------------------------------- [ ] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. [ ] swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes: [ ] ffff80003d7c08d0 (&v3d_priv->stats[i].lock){?.+.}-{0:0}, at: v3d_irq+0xc8/0x660 [v3d] [ ] {HARDIRQ-ON-W} state was registered at: [ ] lock_acquire+0x1f8/0x328 [ ] v3d_job_start_stats.isra.0+0xd8/0x218 [v3d] [ ] v3d_bin_job_run+0x23c/0x388 [v3d] [ ] drm_sched_run_job_work+0x520/0x6d0 [gpu_sched] [ ] process_one_work+0x62c/0xb48 [ ] worker_thread+0x468/0x5b0 [ ] kthread+0x1c4/0x1e0 [ ] ret_from_fork+0x10/0x20 [ ] irq event stamp: 337094 [ ] hardirqs last enabled at (337093): [] default_idle_call+0x11c/0x140 [ ] hardirqs last disabled at (337094): [] el1_interrupt+0x24/0x58 [ ] softirqs last enabled at (337082): [] handle_softirqs+0x4e0/0x538 [ ] softirqs last disabled at (337073): [] __do_softirq+0x1c/0x28 [ ] other info that might help us debug this: [ ] Possible unsafe locking scenario: [ ] CPU0 [ ] ---- [ ] lock(&v3d_priv->stats[i].lock); [ ] [ ] lock(&v3d_priv->stats[i].lock); [ ] *** DEADLOCK *** [ ] no locks held by swapper/0/0. [ ] stack backtrace: [ ] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G WC 6.10.3-v8-16k-numa #159 [ ] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT) [ ] Call trace: [ ] dump_backtrace+0x170/0x1b8 [ ] show_stack+0x20/0x38 [ ] dump_stack_lvl+0xb4/0xd0 [ ] dump_stack+0x18/0x28 [ ] print_usage_bug+0x3cc/0x3f0 [ ] mark_lock+0x4d0/0x968 [ ] __lock_acquire+0x784/0x18c8 [ ] lock_acquire+0x1f8/0x328 [ ] v3d_job_update_stats+0xec/0x2e0 [v3d] [ ] v3d_irq+0xc8/0x660 [v3d] [ ] __handle_irq_event_percpu+0x1f8/0x488 [ ] handle_irq_event+0x88/0x128 [ ] handle_fasteoi_irq+0x298/0x408 [ ] generic_handle_domain_irq+0x50/0x78 But it is a false positive because all the queue-stats pairs have their own lock and jobs are also one at a time. Nevertheless we can appease lockdep by disabling local interrupts to make it see lock usage is consistent. Signed-off-by: Tvrtko Ursulin Fixes: 6abe93b621ab ("drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler") Cc: Maíra Canal --- drivers/gpu/drm/v3d/v3d_sched.c | 44 ++++++++++++++++++++++++++++++--- 1 file changed, 40 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/v3d/v3d_sched.c b/drivers/gpu/drm/v3d/v3d_sched.c index cc2e5a89467b..e4fc3d401edd 100644 --- a/drivers/gpu/drm/v3d/v3d_sched.c +++ b/drivers/gpu/drm/v3d/v3d_sched.c @@ -135,8 +135,31 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *global_stats = &v3d->queue[queue].stats; struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); + unsigned long flags; - preempt_disable(); + /* + * We only need to disable local interrupts to appease lockdep who + * otherwise would think v3d_job_start_stats vs v3d_stats_update has an + * unsafe in-irq vs no-irq-off usage problem. This is a false positive + * becuase all the locks are per queue and stats type, and all jobs are + * completely one at a time serialised. More specifically: + * + * 1. Locks for GPU queues are updated from interrupt handlers under a + * spin lock and started here with preemption disabled. + * + * 2. Locks for CPU queues are updated from the worker with preemption + * disabled and equally started here with preemption disabled. + * + * Therefore both are consistent. + * + * 3. Because next job can only be queued after the previous one has + * been signaled, and locks are per queue, there is also no scope for + * the start part to race with the update part. + */ + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_save(flags); + else + preempt_disable(); write_seqcount_begin(&local_stats->lock); local_stats->start_ns = now; @@ -146,7 +169,10 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) global_stats->start_ns = now; write_seqcount_end(&global_stats->lock); - preempt_enable(); + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_restore(flags); + else + preempt_enable(); } static void @@ -167,11 +193,21 @@ v3d_job_update_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *global_stats = &v3d->queue[queue].stats; struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); + unsigned long flags; + + /* See comment in v3d_job_start_stats() */ + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_save(flags); + else + preempt_disable(); - preempt_disable(); v3d_stats_update(local_stats, now); v3d_stats_update(global_stats, now); - preempt_enable(); + + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_restore(flags); + else + preempt_enable(); } static struct dma_fence *v3d_bin_job_run(struct drm_sched_job *sched_job)