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 4D2A7C25B06 for ; Thu, 11 Aug 2022 16:03:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237016AbiHKQDi (ORCPT ); Thu, 11 Aug 2022 12:03:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237011AbiHKQDM (ORCPT ); Thu, 11 Aug 2022 12:03:12 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA182785A8; Thu, 11 Aug 2022 08:50:19 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 7DD5FCE224D; Thu, 11 Aug 2022 15:49:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54DF8C433C1; Thu, 11 Aug 2022 15:49:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660232980; bh=MAiaC/5yBcdIJnS4EwGQVV4M3oiWPn1vOI6l1WzdSog=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=e0tDevSPU9uLn9bgjHiRVdBc2lHd0lOrKuGrr319QuI5qwTumKDWqWH5eHov1JZW1 7Q2atpu96PkMjLDA3UQj8eGc/2t6JSy1uFAYc9aj9dYOfeklrF9yksCyLzWJfJHXXT h+cH8XIvlhIRBqGflyxptyB85B/UGUoj9Y/uNwDbmlTETuKRi2I4MdQIwn6Mdfwx4/ H2poT0lZYqAp5rUfYUzbsEnLovYhQHLIsnn3eiB35Y7LFn5tGp/PgYQrZBjnEtasV2 BFEWuby7tjpfv+RNx6pYk6IRRkuoYnly/Crl89Br47elrDtmEvVHNizeFOTVs51oWM Zu05NZFf6bUhw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Rob Clark , Sasha Levin , robdclark@gmail.com, quic_abhinavk@quicinc.com, dmitry.baryshkov@linaro.org, airlied@linux.ie, daniel@ffwll.ch, linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org Subject: [PATCH AUTOSEL 5.18 56/93] drm/msm/gem: Drop obj lock in msm_gem_free_object() Date: Thu, 11 Aug 2022 11:41:50 -0400 Message-Id: <20220811154237.1531313-56-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220811154237.1531313-1-sashal@kernel.org> References: <20220811154237.1531313-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org From: Rob Clark [ Upstream commit a414fe3a2129b490e1e9b8ad66f0364f4f961887 ] The only reason we grabbed the lock was to satisfy a bunch of places that WARN_ON() if called without the lock held. But this angers lockdep which doesn't realize no one else can be holding the lock by the time we end up destroying the object (and sees what would otherwise be a locking inversion between reservation_ww_class_mutex and fs_reclaim). Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/14 Signed-off-by: Rob Clark Patchwork: https://patchwork.freedesktop.org/patch/489364/ Link: https://lore.kernel.org/r/20220613205032.2652374-1-robdclark@gmail.com Signed-off-by: Sasha Levin --- drivers/gpu/drm/msm/msm_gem.c | 8 -------- drivers/gpu/drm/msm/msm_gem.h | 14 +++++++++++++- 2 files changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index a4f61972667b..59d5f327047e 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -991,8 +991,6 @@ void msm_gem_free_object(struct drm_gem_object *obj) list_del(&msm_obj->mm_list); mutex_unlock(&priv->mm_lock); - msm_gem_lock(obj); - /* object should not be on active list: */ GEM_WARN_ON(is_active(msm_obj)); @@ -1008,17 +1006,11 @@ void msm_gem_free_object(struct drm_gem_object *obj) put_iova_vmas(obj); - /* dma_buf_detach() grabs resv lock, so we need to unlock - * prior to drm_prime_gem_destroy - */ - msm_gem_unlock(obj); - drm_prime_gem_destroy(obj, msm_obj->sgt); } else { msm_gem_vunmap(obj); put_pages(obj); put_iova_vmas(obj); - msm_gem_unlock(obj); } drm_gem_object_release(obj); diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h index af612add5264..f62855134660 100644 --- a/drivers/gpu/drm/msm/msm_gem.h +++ b/drivers/gpu/drm/msm/msm_gem.h @@ -196,7 +196,19 @@ msm_gem_unlock(struct drm_gem_object *obj) static inline bool msm_gem_is_locked(struct drm_gem_object *obj) { - return dma_resv_is_locked(obj->resv); + /* + * Destroying the object is a special case.. msm_gem_free_object() + * calls many things that WARN_ON if the obj lock is not held. But + * acquiring the obj lock in msm_gem_free_object() can cause a + * locking order inversion between reservation_ww_class_mutex and + * fs_reclaim. + * + * This deadlock is not actually possible, because no one should + * be already holding the lock when msm_gem_free_object() is called. + * Unfortunately lockdep is not aware of this detail. So when the + * refcount drops to zero, we pretend it is already locked. + */ + return dma_resv_is_locked(obj->resv) || (kref_read(&obj->refcount) == 0); } static inline bool is_active(struct msm_gem_object *msm_obj) -- 2.35.1