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 55576C71153 for ; Sat, 2 Sep 2023 18:28:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230488AbjIBS2a (ORCPT ); Sat, 2 Sep 2023 14:28:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229482AbjIBS2a (ORCPT ); Sat, 2 Sep 2023 14:28:30 -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 DECC0E4B for ; Sat, 2 Sep 2023 11:28:26 -0700 (PDT) Received: from [192.168.2.205] (109-252-153-31.dynamic.spd-mgts.ru [109.252.153.31]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id D05AB6607285; Sat, 2 Sep 2023 19:28:23 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693679305; bh=16VQ2EWyfHrq08hQmOsXZjo53afgTw+mo/8RhowkQ2c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Tx6uOIJCIjQW5Me0hvxoAfLLUZU7W8R/FmsBGNuOAFVKodQSurm91/zNrTm4/Qvtp Dlt8ReHbCmj/ch8x8VAU8uJ118uQnGxQ7nhR2WrdBnkdQImvRSANQTpPTZP2K7xYsL TVOSQJoPgIAKNdS/qtjihuYJIcGWrIdd/efTc9dswYbvLQXlf9Ndnnpwz6HIBmcoZM cToMyeQ0YnqGQyRQ3p3t6XzsGsolFKqrvlL/4h/b0a1Pjd5HUK0jn+eTSaY6XfwRE1 c1bNgV27sjZUujSSjfE0go660sPamIHhXPFmmJu3CRXP4L099VExUgR1ZvAmDF28vP exsoma6gymAPQ== Message-ID: <1a40d9c6-fdbf-1494-00f2-1e37206fc984@collabora.com> Date: Sat, 2 Sep 2023 21:28:21 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v15 02/23] drm/shmem-helper: Use flag for tracking page count bumped by get_pages_sgt() Content-Language: en-US To: Boris Brezillon Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , =?UTF-8?Q?Christian_K=c3=b6nig?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-3-dmitry.osipenko@collabora.com> <20230828125518.7b926fc6@collabora.com> From: Dmitry Osipenko In-Reply-To: <20230828125518.7b926fc6@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/28/23 13:55, Boris Brezillon wrote: > On Sun, 27 Aug 2023 20:54:28 +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 | 3 ++- >> drivers/gpu/drm/lima/lima_gem.c | 1 + >> include/drm/drm_gem_shmem_helper.h | 7 +++++++ >> 3 files changed, 10 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c >> index 78d9cf2355a5..db20b9123891 100644 >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c >> @@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) >> sg_free_table(shmem->sgt); >> kfree(shmem->sgt); >> } >> - if (shmem->pages) >> + if (shmem->got_sgt) >> drm_gem_shmem_put_pages(shmem); > > Can't we just move this drm_gem_shmem_put_pages() call in the > if (shmem->sgt) block? As you've seen in patch #1, the shmem->sgt may belong to imported dmabuf and pages aren't referenced in this case. I agree that the freeing code is confusing. The flags make it a better, not ideal. Though, the flags+comments solution is good enough to me. Please let me know if you have more suggestions, otherwise I'll add comment to the code and keep this patch for v16. BTW, I realized that the new flag wasn't placed properly in the Lima driver, causing unbalanced page count in the error path. Will correct it in v16. -- Best regards, Dmitry