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 E3164EB64DD for ; Wed, 12 Jul 2023 12:35:46 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5CEAE10E501; Wed, 12 Jul 2023 12:35:46 +0000 (UTC) Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9490C10E501 for ; Wed, 12 Jul 2023 12:35:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1689165343; x=1720701343; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=jT8JlmUksO7b3moJrWsest0mR7G5qwAdgmjn+UEIx0w=; b=FCUvGwXK1srJCV5TXcsXy5Fe1a9jWJFejfasWixkDNESLS1KkkTX98XW j+xTzkAflDnVDNhyoLRe8duT7XHVUehirwtavF8f7O9NzDhcQ44HfoxWP 3pTbKGJJ9zhvvp2KovEsaiGM2ceul1mHXVsW3ef/EAjFw7UIF7/2620FJ lF6xDRaBNU9HRXdejd/fR+eDLrGs9gnV58CK/fEPUuQOo12ZbrXxfciCw 3CI3sXgTiUGtmrg8veCcWCJdqJ1QbNQ41pT7/BK7ZMtjQvb7DlmwgTRm/ DOqn3KvnAxDoklzFBzvMatpv4OKSM2qLiqC5bVyRl4XbRSLoGX4MyET9s g==; X-IronPort-AV: E=McAfee;i="6600,9927,10769"; a="364911525" X-IronPort-AV: E=Sophos;i="6.01,199,1684825200"; d="scan'208";a="364911525" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2023 05:35:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10769"; a="715565250" X-IronPort-AV: E=Sophos;i="6.01,199,1684825200"; d="scan'208";a="715565250" Received: from eamonnob-mobl1.ger.corp.intel.com (HELO [10.213.237.202]) ([10.213.237.202]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2023 05:35:40 -0700 Message-ID: Date: Wed, 12 Jul 2023 13:35:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Content-Language: en-US To: Andrzej Hajda , Andi Shyti References: <20230705160848.988464-1-andrzej.hajda@intel.com> <20230706151611.1024576-1-andrzej.hajda@intel.com> <118e74c0-c1ce-fc6e-39f4-5518ace5d71e@intel.com> <6f981dd3-715a-6b7e-6c5d-d51610cddc88@linux.intel.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Intel-gfx] [PATCH v2] drm/i915/gt: update request engine before removing virtual GuC 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: , Cc: intel-gfx@lists.freedesktop.org, Chris Wilson , Nirmoy Das Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 12/07/2023 13:18, Andrzej Hajda wrote: > On 11.07.2023 17:27, Tvrtko Ursulin wrote: >> >> On 11/07/2023 14:58, Andrzej Hajda wrote: >>> On 11.07.2023 13:34, Andi Shyti wrote: >>>> Hi Andrzej, >>>> >>>>>           drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 11 >>>>> +++++++++++ >>>>>           1 file changed, 11 insertions(+) >>>>> >>>>>          diff --git >>>>> a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c >>>>> b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c >>>>>          index a0e3ef1c65d246..2c877ea5eda6f0 100644 >>>>>          --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c >>>>>          +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c >>>>>          @@ -3461,6 +3461,8 @@ static void guc_prio_fini(struct >>>>> i915_request *rq, struct intel_context *ce) >>>>>           static void remove_from_context(struct i915_request *rq) >>>>>           { >>>>>                  struct intel_context *ce = >>>>> request_to_scheduling_context(rq); >>>>>          +       struct intel_engine_cs *engine; >>>>>          +       intel_engine_mask_t tmp; >>>>> >>>>>                  GEM_BUG_ON(intel_context_is_child(ce)); >>>>> >>>>>          @@ -3478,6 +3480,15 @@ static void >>>>> remove_from_context(struct i915_request *rq) >>>>> >>>>>                  atomic_dec(&ce->guc_id.ref); >>>>>                  i915_request_notify_execute_cb_imm(rq); >>>>>          + >>>>>          +       /* >>>>>          +        * GuC virtual engine can disappear after this >>>>> call, so let's assign >>>>>          +        * something valid, as driver expects this to be >>>>> always valid pointer. >>>>>          +        */ >>>>>          +       for_each_engine_masked(engine, rq->engine->gt, >>>>> rq->execution_mask, tmp) { >>>>>          +               rq->engine = engine; >>>>> >>>>>      yes... here the context might lose the virtual engine... I wonder >>>>>      whether this is the rigth solution, though. Maybe we should set >>>>>      rq->engine = NULL; and check for NULL? Don't know. >>>>> >>>>> >>>>> Setting NULL causes occasional null page de-reference in >>>>> >>>>> i915_request_wait_timeout: >>>>> >>>>> mutex_release(&rq->engine->gt->reset.mutex.dep_map, _THIS_IP_) >>>>> >>>>> rq->engine after removing rq from context is (IMHO) used as a set >>>>> of aliases >>>>> for gt and i915 (despite rq itself contains the alias to i915). >>>> without investigating further, but maybe that code is not even >>>> supposed to be executed, at this point, if the request's assigned >>>> virtual engine is removed. >>> >>> Real tests show it is executed and the function >>> i915_request_wait_timeout is quite generic >>> I guess it is quite typical use-case, the only question is about >>> timings - what happens earlier - >>> finalization of i915_request_wait_timeout or context removal. >>> >>> The other point rq->engine is accessed after context removal is >>> i915_fence_release - >>> there is long comment there regarding virtual context and reuse >>> retired rq. >>> Anyway calling there "intel_engine_is_virtual(rq->engine)" is risky >>> without this patch and KASAN complains clearly about it: >>> http://gfx-ci.igk.intel.com/tree/drm-tip/kasan.html?testfilter=gem_exec_balancer >> >> Looks like a bug introduced in bcb9aa45d5a0 ("Revert "drm/i915: Hold >> reference to intel_context over life of i915_request""), which was a >> partial revert of 1e98d8c52ed5 ("drm/i915: Hold reference to >> intel_context over life of i915_request"). >> >> Ie. if 1e98d8c52ed5 recognised the problem with disappearing >> rq->engine, then I am confused how bcb9aa45d5a0 left the rq->engine >> dereference in there after removing the extra reference. >> >> Could it be that the intel_engine_is_virtual check simply needs to be >> removed from i915_fence_release, restoring things to how they were >> before 1e98d8c52ed5? Could you try it out? > > > I have already tried something similar [1] and KASAN bugs disappeared, > or more precisely gem_exec_balance tests passed. But I have been warned > by Nirmoy guc virtual engines can be created for only one real engine > (ie. is_power_of_2(rq->execution_mask) is true but rq->engine points to > virtual engine). > > [1]: https://patchwork.freedesktop.org/series/118879/ Ugh.. Try involving media umd folks to see if they need a single engine virtual engine? Or we could always just not create it in the driver, I mean just use the physical one. Regards, Tvrtko