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 E62E7C63777 for ; Wed, 18 Nov 2020 11:38:49 +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 8486D20B80 for ; Wed, 18 Nov 2020 11:38:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8486D20B80 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 B66C46E3F5; Wed, 18 Nov 2020 11:38:48 +0000 (UTC) Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by gabe.freedesktop.org (Postfix) with ESMTPS id E27966E3F5 for ; Wed, 18 Nov 2020 11:38:46 +0000 (UTC) IronPort-SDR: ragpwL9kGxpDF87EabKX92BnPPqQKFyUqxOe99NhFsJM5kBSj+wgzsmqWW3jkl0uMJsBsbAlNz sL519uVfLCvw== X-IronPort-AV: E=McAfee;i="6000,8403,9808"; a="150948398" X-IronPort-AV: E=Sophos;i="5.77,486,1596524400"; d="scan'208";a="150948398" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Nov 2020 03:38:46 -0800 IronPort-SDR: 7fk/PxkLE+D9XPpvQ6a+43cslaMgL3mlVkxbUpkBO5+T8WTgSK8NgyxLbVojFd5xQDP8Y7TOAd Op8bbFUJrphw== X-IronPort-AV: E=Sophos;i="5.77,486,1596524400"; d="scan'208";a="544481569" 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 03:38:45 -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> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc Message-ID: Date: Wed, 18 Nov 2020 11:38:43 +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: <160569868396.3553.1145860250763004021@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 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? > I observed the leaked ve->request, but the tasklet_kill, iirc, is > speculation about possible windows. Admittedly all long test runs have > been with this patch in place for most of the last year. > >>> + /* 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. > > Some might say I was fixing up an earlier oversight. Separate patch would be good, with Fixes: probably since it is a memory leak and one liner. Regards, Tvrtko _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx