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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0FADCA0FFA for ; Tue, 5 Sep 2023 16:51:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234094AbjIEQvA (ORCPT ); Tue, 5 Sep 2023 12:51:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353729AbjIEHk6 (ORCPT ); Tue, 5 Sep 2023 03:40:58 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23CB21A8 for ; Tue, 5 Sep 2023 00:40:55 -0700 (PDT) Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id 1C2B766028F5; Tue, 5 Sep 2023 08:40:53 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693899653; bh=MMtwZSS4hAHlzfbMlS/VKZ1O76qe9W6PnspTivVDuWA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=B3JctmSNqpV709VZaf7ywJ4+xd8I1iG3MdkG/7wYLuviVhmz2Ld6WaW645AkFHWYO PoEaUo35CD3y/VtNQ8a5cwMwd5BSG7vd2CNXFm8lm+7tU76jnCVCaX6qkYZpuibrgF X9tRnaYw/FlTpG3RTzlj3zJTFXk/vmfbGXrDewUpe3Kj5mSgG0wlkdjm6WYKLTsuKL eozOt/j1Xp03SoctIPp0bxjsgoAWe/BZQwoG6ktXRyzVLpZjuEfW1qcR9Q66bubC2r fJi1Cu580Rq57DNjkSCmPEnPDiZMYTHJVcNDKMIQIVC9HHBbqEYMv81hsigui2Pllj 2+EM0ZZ+oYyLg== Date: Tue, 5 Sep 2023 09:40:50 +0200 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v16 02/20] drm/shmem-helper: Use flag for tracking page count bumped by get_pages_sgt() Message-ID: <20230905094050.3c918a43@collabora.com> In-Reply-To: <20230903170736.513347-3-dmitry.osipenko@collabora.com> References: <20230903170736.513347-1-dmitry.osipenko@collabora.com> <20230903170736.513347-3-dmitry.osipenko@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 3 Sep 2023 20:07:18 +0300 Dmitry Osipenko wrote: > Use separate flag for tracking page count bumped by shmem->sgt to avoid > imbalanced page counter during of drm_gem_shmem_free() time. It's fragile > to assume that populated shmem->pages at a freeing time means that the > count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes > the ambiguity. > > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 11 ++++++++++- > drivers/gpu/drm/lima/lima_gem.c | 1 + > include/drm/drm_gem_shmem_helper.h | 7 +++++++ > 3 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 6693d4061ca1..848435e08eb2 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -152,8 +152,10 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > sg_free_table(shmem->sgt); > kfree(shmem->sgt); > } > - if (shmem->pages) > + if (shmem->pages) { > drm_gem_shmem_put_pages(shmem); > + drm_WARN_ON(obj->dev, !shmem->got_pages_sgt); > + } Already mentioned in v15, but I keep thinking the following: if (shmem->sgt) { // existing code in the preceding // if (shmem->sgt) branch ... /* * Release the implicit pages ref taken in * drm_gem_shmem_get_pages_sgt_locked(). */ drm_gem_shmem_put_pages(shmem); } does exactly the same without requiring the addition of a new field. > > drm_WARN_ON(obj->dev, shmem->pages_use_count); > > @@ -693,6 +695,13 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_ > if (ret) > goto err_free_sgt; > > + /* > + * This flag prevents imbalanced pages_use_count during > + * drm_gem_shmem_free(), where pages_use_count=1 only if > + * drm_gem_shmem_get_pages_sgt() was used by a driver. > + */ > + shmem->got_pages_sgt = true; > + > shmem->sgt = sgt; > > return sgt; > diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c > index 4f9736e5f929..67c39b95e30e 100644 > --- a/drivers/gpu/drm/lima/lima_gem.c > +++ b/drivers/gpu/drm/lima/lima_gem.c > @@ -48,6 +48,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) > > bo->base.pages = pages; > bo->base.pages_use_count = 1; > + bo->base.got_pages_sgt = true; > > mapping_set_unevictable(mapping); > } > diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h > index ec70a98a8fe1..a53c0874b3c4 100644 > --- a/include/drm/drm_gem_shmem_helper.h > +++ b/include/drm/drm_gem_shmem_helper.h > @@ -73,6 +73,13 @@ struct drm_gem_shmem_object { > */ > unsigned int vmap_use_count; > > + /** > + * @got_pages_sgt: > + * > + * True if SG table was retrieved using drm_gem_shmem_get_pages_sgt() > + */ > + bool got_pages_sgt : 1; > + > /** > * @imported_sgt: > *