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 4D108C5519F for ; Wed, 18 Nov 2020 11:05:33 +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 BA42322228 for ; Wed, 18 Nov 2020 11:05:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA42322228 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 2AD7288843; Wed, 18 Nov 2020 11:05:30 +0000 (UTC) Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6506588843 for ; Wed, 18 Nov 2020 11:05:29 +0000 (UTC) IronPort-SDR: VPF43e6uJ6Ib8+tTYHph1zy9ktx8QanNNXTxfZv3mpC9UwQcd8kSxvlypVuLsHi+9Rd+k8WBJi jYbpZPu/w50g== X-IronPort-AV: E=McAfee;i="6000,8403,9808"; a="235246427" X-IronPort-AV: E=Sophos;i="5.77,486,1596524400"; d="scan'208";a="235246427" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Nov 2020 03:05:28 -0800 IronPort-SDR: z3p9cQEKa55pGQw58DWAqUCQBml1+rjJqwBbjZYmcbGD0p60q5x6EzFnvbKzrH7vGivLam7R3C HT7eYzo/bIKw== X-IronPort-AV: E=Sophos;i="5.77,486,1596524400"; d="scan'208";a="544467806" Received: from shaid-mobl.ger.corp.intel.com (HELO [10.255.202.56]) ([10.255.202.56]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Nov 2020 03:05:27 -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> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc Message-ID: <86cb67d0-ac39-7f83-8ff8-eed3ef7c5943@linux.intel.com> Date: Wed, 18 Nov 2020 11:05:24 +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: <20201117113103.21480-14-chris@chris-wilson.co.uk> 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 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? > + > + /* Decouple ourselves from the siblings, no more access allowed. */ > for (n = 0; n < ve->num_siblings; n++) { > struct intel_engine_cs *sibling = ve->siblings[n]; > struct rb_node *node = &ve->nodes[sibling->id].rb; > - unsigned long flags; > > if (RB_EMPTY_NODE(node)) > continue; > > - spin_lock_irqsave(&sibling->active.lock, flags); > + spin_lock_irq(&sibling->active.lock); > > /* Detachment is lazily performed in the execlists tasklet */ > if (!RB_EMPTY_NODE(node)) > rb_erase_cached(node, &sibling->execlists.virtual); > > - spin_unlock_irqrestore(&sibling->active.lock, flags); > + spin_unlock_irq(&sibling->active.lock); > } > GEM_BUG_ON(__tasklet_is_scheduled(&ve->base.execlists.tasklet)); > + GEM_BUG_ON(!list_empty(virtual_queue(ve))); > > if (ve->context.state) > __execlists_context_fini(&ve->context); > intel_context_fini(&ve->context); > > intel_engine_free_request_pool(&ve->base); > + intel_breadcrumbs_free(ve->base.breadcrumbs); This looks to belong to some other patch. Regards, Tvrtko > > kfree(ve->bonds); > kfree(ve); > } > > +static void virtual_context_destroy(struct kref *kref) > +{ > + struct virtual_engine *ve = > + container_of(kref, typeof(*ve), context.ref); > + > + GEM_BUG_ON(!list_empty(&ve->context.signals)); > + > + /* > + * When destroying the virtual engine, we have to be aware that > + * it may still be in use from an hardirq/softirq context causing > + * the resubmission of a completed request (background completion > + * due to preempt-to-busy). Before we can free the engine, we need > + * to flush the submission code and tasklets that are still potentially > + * accessing the engine. Flushing the tasklets require process context, > + * and since we can guard the resubmit onto the engine with an RCU read > + * lock, we can delegate the free of the engine to an RCU worker. > + */ > + INIT_RCU_WORK(&ve->rcu, rcu_virtual_context_destroy); > + queue_rcu_work(system_wq, &ve->rcu); > +} > + > static void virtual_engine_initial_hint(struct virtual_engine *ve) > { > int swp; > _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx