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 8D13CEB48FC for ; Thu, 12 Feb 2026 11:07:46 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E12FD10E237; Thu, 12 Feb 2026 11:07:45 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=collabora.com header.i=@collabora.com header.b="d//CJP6j"; dkim-atps=neutral Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2FEB910E237 for ; Thu, 12 Feb 2026 11:07:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1770894462; bh=E/k4M4KrO5oPdNQ6TyxoTcbl0HWeRZk7Wtw8a3OrLkA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=d//CJP6j1EC6lohf6+ipyUdcOZUBKA6g90DJssorKLQJ2GGLvgxF5ylXt9KMxq937 AH82D/yRbIoMUb7qNfrPqS66udA/dXrYMeBFgTXFEBh9k20QzHHs/sPLWB0TJpfvIu Fb4jiQZO7XofJubC4CzH7SH4Qyze/JvwWpeXATlg3T4ZLvO83YJOCLplPs4o61j0zf IpQAEEnJpdD7iELOdFSTHlC0OXw3tM0awZ+oJ8kIzDxQ1Fk8Aw1ZRGnE16u06RFFpm HSiPoqBAycKQkQoBv264aGXMzii9vkw+yrU1RbXgEgbQaW3sZwYAh+AOGStxhd6qbM jyvA3uYaOIu6g== Received: from fedora (unknown [IPv6:2a01:e0a:2c:6930:d919:a6e:5ea1:8a9f]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 0FB4817E0A49; Thu, 12 Feb 2026 12:07:42 +0100 (CET) Date: Thu, 12 Feb 2026 12:07:38 +0100 From: Boris Brezillon To: Steven Price Cc: Liviu Dudau , =?UTF-8?B?QWRyacOhbg==?= Larumbe , dri-devel@lists.freedesktop.org, David Airlie , Simona Vetter , Akash Goel , Rob Clark , Sean Paul , Konrad Dybcio , Akhil P Oommen , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Dmitry Osipenko , Chris Diamand , Danilo Krummrich , Matthew Brost , Thomas =?UTF-8?B?SGVsbHN0csO2bQ==?= , Alice Ryhl , kernel@collabora.com Subject: Re: [PATCH v3 5/9] drm/panthor: Part ways with drm_gem_shmem_object Message-ID: <20260212120738.57cc1655@fedora> In-Reply-To: <4f90ca0b-4291-43a8-b131-19da3ac848e9@arm.com> References: <20260211080343.1887134-1-boris.brezillon@collabora.com> <20260211080343.1887134-6-boris.brezillon@collabora.com> <4f90ca0b-4291-43a8-b131-19da3ac848e9@arm.com> Organization: Collabora X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, 11 Feb 2026 15:58:27 +0000 Steven Price wrote: > On 11/02/2026 08:03, Boris Brezillon wrote: > > While drm_gem_shmem_object does most of the job we need it to do, the > > way sub-resources (pages, sgt, vmap) are handled and their lifetimes > > gets in the way of BO reclaim. There has been attempts to address > > that [1], but in the meantime, new gem_shmem users were introduced > > (accel drivers), and some of them manually free some of these resources. > > This makes things harder to control/sanitize/validate. > > > > Thomas Zimmerman is not a huge fan of enforcing lifetimes of sub-resources > > and forcing gem_shmem users to go through new gem_shmem helpers when they > > need manual control of some sort, and I believe this is a dead end if > > we don't force users to follow some stricter rules through carefully > > designed helpers, because there will always be one user doing crazy things > > with gem_shmem_object internals, which ends up tripping out the common > > helpers when they are called. > > > > The consensus we reached was that we would be better off forking > > gem_shmem in panthor. So here we are, parting ways with gem_shmem. The > > current transition tries to minimize the changes, but there are still > > some aspects that are different, the main one being that we no longer > > have a pages_use_count, and pages stays around until the GEM object is > > destroyed (or when evicted once we've added a shrinker). The sgt also > > no longer retains pages. This is losely based on how msm does things by > > the way. > > > > If there's any interest in sharing code (probably with msm, since the > > panthor shrinker is going to be losely based on the msm implementation), > > we can always change gears and do that once we have everything > > working/merged. > > > > [1]https://patchwork.kernel.org/project/dri-devel/patch/20240105184624.508603-1-dmitry.osipenko@collabora.com/ > > > > v2: > > - Fix refcounting > > - Add a _locked suffix to a bunch of functions expecting the resv lock > > to be held > > - Take the lock before releasing resources in panthor_gem_free_object() > > > > v3: > > - Use ERR_CAST() to fix an ERR-ptr deref > > - Add missing resv_[un]lock() around a panthor_gem_backing_unpin_locked() > > call > > > > Signed-off-by: Boris Brezillon > > Looks good, but one issue I missed previously below. > > [...] > > > + > > +static void * > > +panthor_gem_vmap_get_locked(struct panthor_gem_object *bo) > > +{ > > + pgprot_t prot = PAGE_KERNEL; > > + void *vaddr; > > + int ret; > > + > > + dma_resv_assert_held(bo->base.resv); > > + > > + if (drm_WARN_ON_ONCE(bo->base.dev, drm_gem_is_imported(&bo->base))) > > + return ERR_PTR(-EINVAL); > > + > > + if (refcount_inc_not_zero(&bo->cmap.vaddr_use_count)) { > > + drm_WARN_ON_ONCE(bo->base.dev, !bo->cmap.vaddr); > > + return bo->cmap.vaddr; > > + } > > + > > + ret = panthor_gem_backing_pin_locked(bo); > > + if (ret) > > + return ERR_PTR(ret); > > + > > + ret = panthor_gem_prep_for_cpu_map_locked(bo); > > + if (ret) > > + return ERR_PTR(ret); > > This should be "goto err_unpin" to drop the pin. Oops, will fix in v4.