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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 0C809C54FCB for ; Mon, 20 Apr 2020 16:15:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA466206F6 for ; Mon, 20 Apr 2020 16:15:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726412AbgDTQPS (ORCPT ); Mon, 20 Apr 2020 12:15:18 -0400 Received: from mail-pj1-f66.google.com ([209.85.216.66]:54897 "EHLO mail-pj1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725958AbgDTQPS (ORCPT ); Mon, 20 Apr 2020 12:15:18 -0400 Received: by mail-pj1-f66.google.com with SMTP id np9so53109pjb.4; Mon, 20 Apr 2020 09:15:17 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=mKMIW3mEg5t1gLoJ6mz8YW5V5YHdFX18CfmBOsT8+DM=; b=f7Ti89jI8mxJ++RbVIzArU4aCIEPh2c72uCntV4+3RouLxK7sEZBvt+6OnCYrx6e4c MdFybnbC7fdPiafrm3LmvP1xu/0VFNOkVfnV5Y35HpjYxocBMleKj1IUrIma8cc4LYuY XO67BjJrs5if1zVZGqpE23u8n10aS5YSECe3URm61+tcpnisZgsPZU2BsHcjpsYbhe9T ZXvbiVZLFSJLP23APR0r6aBIujdvAfQZBLRDyqlj4rCeqoV9TkvbuIo6fN9fcZ9g0oox FKqujgWDDMAitHe/ewdxdInmeJwAlBaHKl7rS9WPewzyqBZC7je0tIt+TvchrFLe1TRF 7pmA== X-Gm-Message-State: AGi0Pub8xibp06D0DzIgpYwu1wm2LyA1NuuxSHnaeNITk6Pi5CxphHwF oFqZyM52QOIvakJPOxp3O6jcVnfw X-Google-Smtp-Source: APiQypIo65I60EmrvJr0Fn9k464/b4BsdAENW1ihErA04xVYqn/vV5ywXSVnzlYGX6PHk/VUYYyFKA== X-Received: by 2002:a17:90a:890a:: with SMTP id u10mr161799pjn.154.1587399317254; Mon, 20 Apr 2020 09:15:17 -0700 (PDT) Received: from sultan-box.localdomain ([104.200.129.62]) by smtp.gmail.com with ESMTPSA id o1sm48749pjs.35.2020.04.20.09.15.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Apr 2020 09:15:16 -0700 (PDT) Date: Mon, 20 Apr 2020 09:15:14 -0700 From: Sultan Alsawaf To: Joonas Lahtinen Cc: Chris Wilson , stable@vger.kernel.org, Jani Nikula , Rodrigo Vivi , David Airlie , Daniel Vetter , Matthew Auld , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] drm/i915: Synchronize active and retire callbacks Message-ID: <20200420161514.GB1963@sultan-box.localdomain> References: <20200404024156.GA10382@sultan-box.localdomain> <20200407064007.7599-1-sultan@kerneltoast.com> <20200414061312.GA90768@sultan-box.localdomain> <158685263618.16269.9317893477736764675@build.alporthouse.com> <20200414144309.GB2082@sultan-box.localdomain> <20200420052419.GA40250@sultan-box.localdomain> <158737090265.8380.6644489879531344891@jlahtine-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <158737090265.8380.6644489879531344891@jlahtine-desk.ger.corp.intel.com> Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Apr 20, 2020 at 11:21:42AM +0300, Joonas Lahtinen wrote: > So it seems that the patch got pulled into v5.6 and has been backported > to v5.5 but not v5.4. You're right, that's my mistake. > In doing that zeroing of ring->vaddr is removed so the test to do mdelay(1) > and "ring->vaddr = NULL;" is not correct. I'm not so sure about this. Look at where `ring->vaddr` is assigned: -------------------------------------8<----------------------------------------- ret = i915_vma_pin(vma, 0, 0, flags); if (unlikely(ret)) goto err_unpin; if (i915_vma_is_map_and_fenceable(vma)) addr = (void __force *)i915_vma_pin_iomap(vma); else addr = i915_gem_object_pin_map(vma->obj, i915_coherent_map_type(vma->vm->i915)); if (IS_ERR(addr)) { ret = PTR_ERR(addr); goto err_ring; } i915_vma_make_unshrinkable(vma); /* Discard any unused bytes beyond that submitted to hw. */ intel_ring_reset(ring, ring->emit); ring->vaddr = addr; ------------------------------------->8----------------------------------------- And then the converse of that is done *before* my reproducer patch does `ring->vaddr = NULL;`: -------------------------------------8<----------------------------------------- i915_vma_unset_ggtt_write(vma); if (i915_vma_is_map_and_fenceable(vma)) i915_vma_unpin_iomap(vma); else i915_gem_object_unpin_map(vma->obj); /* mdelay(1); ring->vaddr = NULL; */ i915_vma_make_purgeable(vma); i915_vma_unpin(vma); ------------------------------------->8----------------------------------------- Isn't the value assigned to `ring->vaddr` trashed by those function calls above where I've got the mdelay? If so, why would it be correct to let the stale value sit in `ring->vaddr`? My interpretation of the zeroing of ring->vaddr being removed by Chris was that it was an unnecessary step before the ring was getting discarded anyway. Sultan