From patchwork Wed Nov 22 20:39:28 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Boris BREZILLON X-Patchwork-Id: 10070931 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 455FB60353 for ; Wed, 22 Nov 2017 20:39:40 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 38E9B29DAA for ; Wed, 22 Nov 2017 20:39:40 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2D97329E3D; Wed, 22 Nov 2017 20:39:40 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 6EBAA29DAA for ; Wed, 22 Nov 2017 20:39:38 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C08D26E6B1; Wed, 22 Nov 2017 20:39:37 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail.free-electrons.com (mail.free-electrons.com [62.4.15.54]) by gabe.freedesktop.org (Postfix) with ESMTP id BCD526E6B1 for ; Wed, 22 Nov 2017 20:39:36 +0000 (UTC) Received: by mail.free-electrons.com (Postfix, from userid 110) id 612DA20989; Wed, 22 Nov 2017 21:39:35 +0100 (CET) Received: from localhost.localdomain (91-160-177-164.subs.proxad.net [91.160.177.164]) by mail.free-electrons.com (Postfix) with ESMTPSA id C89B4203A1; Wed, 22 Nov 2017 21:39:34 +0100 (CET) From: Boris Brezillon To: Eric Anholt Subject: [PATCH] drm/vc4: Fix false positive WARN() backtrace on refcount_inc() usage Date: Wed, 22 Nov 2017 21:39:28 +0100 Message-Id: <20171122203928.28135-1-boris.brezillon@free-electrons.com> X-Mailer: git-send-email 2.11.0 Cc: David Airlie , Stefan Wahren , dri-devel@lists.freedesktop.org, Boris Brezillon X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP With CONFIG_REFCOUNT_FULL enabled, refcount_inc() complains when it's passed a refcount object that has its counter set to 0. In this driver, this is a valid use case since we want to increment ->usecnt only when the BO object starts to be used by real HW components and this is definitely not the case when the BO is created. Fix the problem by using refcount_inc_not_zero() instead of refcount_inc() and fallback to refcount_set(1) when refcount_inc_not_zero() returns false. Note that this 2-steps operation is not racy here because the whole section is protected by a mutex which guarantees that the counter does not change between the refcount_inc_not_zero() and refcount_set() calls. Fixes: b9f19259b84d ("drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl") Reported-by: Stefan Wahren Signed-off-by: Boris Brezillon --- drivers/gpu/drm/vc4/vc4_bo.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c index 4ae45d7dac42..2decc8e2c79f 100644 --- a/drivers/gpu/drm/vc4/vc4_bo.c +++ b/drivers/gpu/drm/vc4/vc4_bo.c @@ -637,7 +637,8 @@ int vc4_bo_inc_usecnt(struct vc4_bo *bo) mutex_lock(&bo->madv_lock); switch (bo->madv) { case VC4_MADV_WILLNEED: - refcount_inc(&bo->usecnt); + if (!refcount_inc_not_zero(&bo->usecnt)) + refcount_set(&bo->usecnt, 1); ret = 0; break; case VC4_MADV_DONTNEED: