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 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 DF99FFCE095 for ; Thu, 26 Feb 2026 14:39:02 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 7756C10E965; Thu, 26 Feb 2026 14:39:02 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; secure) header.d=linutronix.de header.i=@linutronix.de header.b="dUyjoKS3"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="pkwh6iuu"; dkim-atps=neutral Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by gabe.freedesktop.org (Postfix) with ESMTPS id 82D2710E965; Thu, 26 Feb 2026 14:39:01 +0000 (UTC) Date: Thu, 26 Feb 2026 15:38:57 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1772116738; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qD3+6POXKNawLzIUuj2U309vx3UvgtoIfk7xn2TbokQ=; b=dUyjoKS3qrtrq3xWSwNltNQhKE3o4ALW1ajwOY7nqMMCsXtZPKu6siKbP7Cw4YHXOFHRhC e4D1mBMHOiVArrXPRxwOgxruvmhth4wVfL/+Z1odokwiQuMnGZa16FVPXFeZ7zl61xxI7d /Vg2dcH2CDFWfEaD8yZPJWyoTVzEkQdl8SSKbEL/Cuj1gcj6LD4d67NTy/JxeGrXGEuVFM Bkyt8KJHZrus4LasFa48Dye32bn83BWKmoad4egODdq2SnG6NvGwGGkLh61mZTo1MA8UMv I1u4N3q3wsMqfeAMdGv7S+NZq4a94iA0QxzYljVyKijtZyRYYDOSQ+kYWhlCVw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1772116738; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qD3+6POXKNawLzIUuj2U309vx3UvgtoIfk7xn2TbokQ=; b=pkwh6iuuR7s/oYhiqToSdazOZCtQLovdcZtbccX9MNRgHlUHKExkYyYmFExj/bdgS/tOTS RnQ9pkoJopgzepDQ== From: Sebastian Andrzej Siewior To: Maarten Lankhorst Cc: intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-rt-devel@lists.linux.dev, dri-devel@lists.freedesktop.org Subject: Re: [i915-rt v6 00/24] drm/i915/display: All patches to make PREEMPT_RT work on i915 + xe. Message-ID: <20260226143857.4ZJAFzf6@linutronix.de> References: <20260220083657.28815-26-dev@lankhorst.se> <20260224162703.Q_taYjEC@linutronix.de> <20260224165903.2mn24oQy@linutronix.de> <20260225075806.XNtXjZ5E@linutronix.de> <7ee8b784-a714-4329-aab2-a571f25c3baa@lankhorst.se> <20260226120715.6Ug1Qkse@linutronix.de> <20260226141942.Z6vUrEQ3@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260226141942.Z6vUrEQ3@linutronix.de> X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 2026-02-26 15:19:42 [+0100], To Maarten Lankhorst wrote: > On 2026-02-26 13:07:18 [+0100], To Maarten Lankhorst wrote: > > series somewhere I could pull and check. In meantime I would look what > > causes the lockup on i915. > > I think I got it. This the atomic sync as-is, IRQ-Work (FIFO-1) will be preempted by the threaded-interrupt (FIFO-50) and the interrupt will poll on signaler_active while the irq-work can't make progress. This will provide the needed sync: diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index a2b413982ce64..337f6e88faf05 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -209,6 +209,7 @@ static void signal_irq_work(struct irq_work *work) intel_breadcrumbs_disarm_irq(b); rcu_read_lock(); + spin_lock(&b->signaler_active_sync); atomic_inc(&b->signaler_active); list_for_each_entry_rcu(ce, &b->signalers, signal_link) { struct i915_request *rq; @@ -246,6 +247,7 @@ static void signal_irq_work(struct irq_work *work) } } atomic_dec(&b->signaler_active); + spin_unlock(&b->signaler_active_sync); rcu_read_unlock(); llist_for_each_safe(signal, sn, signal) { @@ -290,6 +292,7 @@ intel_breadcrumbs_create(struct intel_engine_cs *irq_engine) init_llist_head(&b->signaled_requests); spin_lock_init(&b->irq_lock); + spin_lock_init(&b->signaler_active_sync); init_irq_work(&b->irq_work, signal_irq_work); b->irq_engine = irq_engine; @@ -487,8 +490,11 @@ void intel_context_remove_breadcrumbs(struct intel_context *ce, if (release) intel_context_put(ce); - while (atomic_read(&b->signaler_active)) + while (atomic_read(&b->signaler_active)) { + spin_lock(&b->signaler_active_sync); + spin_unlock(&b->signaler_active_sync); cpu_relax(); + } } static void print_signals(struct intel_breadcrumbs *b, struct drm_printer *p) diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h index bdf09fd67b6e7..28dae32628aab 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h @@ -40,6 +40,7 @@ struct intel_breadcrumbs { struct list_head signalers; struct llist_head signaled_requests; atomic_t signaler_active; + spinlock_t signaler_active_sync; spinlock_t irq_lock; /* protects the interrupt from hardirq context */ struct irq_work irq_work; /* for use from inside irq_lock */ Sebastian