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=-14.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,HK_RANDOM_FROM,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 3CD51C2D0E4 for ; Thu, 19 Nov 2020 14:06:08 +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 B704C24698 for ; Thu, 19 Nov 2020 14:06:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B704C24698 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2E9316E52C; Thu, 19 Nov 2020 14:06:07 +0000 (UTC) Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0AD406E52C for ; Thu, 19 Nov 2020 14:06:05 +0000 (UTC) IronPort-SDR: lScUCcWtyuo5QqDphwqNn4ISht5KoOK0fG3LeGpmGg/QeFoAMWQcMm8N9QIJTw70C+og8oROns 5SK5TAWQ76ig== X-IronPort-AV: E=McAfee;i="6000,8403,9809"; a="235440394" X-IronPort-AV: E=Sophos;i="5.77,490,1596524400"; d="scan'208";a="235440394" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2020 06:06:05 -0800 IronPort-SDR: Wq9LB+E01q9GfNB7sX3+1tDa9VU5rQUpFiMLsf04+7ic3VGyTAI4P18terDchnwNWVGVKqUNGZ YqLir5ypBfAA== X-IronPort-AV: E=Sophos;i="5.77,490,1596524400"; d="scan'208";a="534788964" Received: from staskuzm-mobl1.ger.corp.intel.com (HELO [10.249.92.37]) ([10.249.92.37]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2020 06:06:03 -0800 To: Chris Wilson , intel-gfx@lists.freedesktop.org References: <20201117113103.21480-1-chris@chris-wilson.co.uk> <20201117113103.21480-14-chris@chris-wilson.co.uk> <86cb67d0-ac39-7f83-8ff8-eed3ef7c5943@linux.intel.com> <160569868396.3553.1145860250763004021@build.alporthouse.com> <160570140499.3553.14837272178441325470@build.alporthouse.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc Message-ID: Date: Thu, 19 Nov 2020 14:06:00 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <160570140499.3553.14837272178441325470@build.alporthouse.com> Content-Language: en-US Subject: Re: [Intel-gfx] [PATCH 14/28] drm/i915/gt: Free stale request on destroying the virtual engine 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: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 18/11/2020 12:10, Chris Wilson wrote: > Quoting Tvrtko Ursulin (2020-11-18 11:38:43) >> >> On 18/11/2020 11:24, Chris Wilson wrote: >>> Quoting Tvrtko Ursulin (2020-11-18 11:05:24) >>>> >>>> On 17/11/2020 11:30, Chris Wilson wrote: >>>>> Since preempt-to-busy, we may unsubmit a request while it is still on >>>>> the HW and completes asynchronously. That means it may be retired and in >>>>> the process destroy the virtual engine (as the user has closed their >>>>> context), but that engine may still be holding onto the unsubmitted >>>>> compelted request. Therefore we need to potentially cleanup the old >>>>> request on destroying the virtual engine. We also have to keep the >>>>> virtual_engine alive until after the sibling's execlists_dequeue() have >>>>> finished peeking into the virtual engines, for which we serialise with >>>>> RCU. >>>>> >>>>> v2: Be paranoid and flush the tasklet as well. >>>>> v3: And flush the tasklet before the engines, as the tasklet may >>>>> re-attach an rb_node after our removal from the siblings. >>>>> >>>>> Signed-off-by: Chris Wilson >>>>> Cc: Tvrtko Ursulin >>>>> --- >>>>> drivers/gpu/drm/i915/gt/intel_lrc.c | 61 +++++++++++++++++++++++++---- >>>>> 1 file changed, 54 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c >>>>> index 17cb7060eb29..c11433884cf6 100644 >>>>> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c >>>>> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c >>>>> @@ -182,6 +182,7 @@ >>>>> struct virtual_engine { >>>>> struct intel_engine_cs base; >>>>> struct intel_context context; >>>>> + struct rcu_work rcu; >>>>> >>>>> /* >>>>> * We allow only a single request through the virtual engine at a time >>>>> @@ -5470,44 +5471,90 @@ static struct list_head *virtual_queue(struct virtual_engine *ve) >>>>> return &ve->base.execlists.default_priolist.requests[0]; >>>>> } >>>>> >>>>> -static void virtual_context_destroy(struct kref *kref) >>>>> +static void rcu_virtual_context_destroy(struct work_struct *wrk) >>>>> { >>>>> struct virtual_engine *ve = >>>>> - container_of(kref, typeof(*ve), context.ref); >>>>> + container_of(wrk, typeof(*ve), rcu.work); >>>>> unsigned int n; >>>>> >>>>> - GEM_BUG_ON(!list_empty(virtual_queue(ve))); >>>>> - GEM_BUG_ON(ve->request); >>>>> GEM_BUG_ON(ve->context.inflight); >>>>> >>>>> + /* Preempt-to-busy may leave a stale request behind. */ >>>>> + if (unlikely(ve->request)) { >>>>> + struct i915_request *old; >>>>> + >>>>> + spin_lock_irq(&ve->base.active.lock); >>>>> + >>>>> + old = fetch_and_zero(&ve->request); >>>>> + if (old) { >>>>> + GEM_BUG_ON(!i915_request_completed(old)); >>>>> + __i915_request_submit(old); >>>>> + i915_request_put(old); >>>>> + } >>>>> + >>>>> + spin_unlock_irq(&ve->base.active.lock); >>>>> + } >>>>> + >>>>> + /* >>>>> + * Flush the tasklet in case it is still running on another core. >>>>> + * >>>>> + * This needs to be done before we remove ourselves from the siblings' >>>>> + * rbtrees as in the case it is running in parallel, it may reinsert >>>>> + * the rb_node into a sibling. >>>>> + */ >>>>> + tasklet_kill(&ve->base.execlists.tasklet); >>>> >>>> Can it still be running after an RCU period? >>> >>> I think there is a window between checking to see if the request is >>> completed and kicking the tasklet, that is not under the rcu lock and >>> opportunity for the request to be retired, and barrier flushed to drop >>> the context references. >> >> From where would that check come? > > The window of opportunity extends all the way from the > i915_request_completed check during unsubmit right until the virtual > engine tasklet is executed -- we do not hold a reference to the virtual > engine for the tasklet, and that request may be retired in the > background, and along with it the virtual engine destroyed. In this case aren't sibling tasklets also a problem? Regards, Tvrtko _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx