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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27062C432C0 for ; Fri, 29 Nov 2019 14:33:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 042982176D for ; Fri, 29 Nov 2019 14:33:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726871AbfK2OdP (ORCPT ); Fri, 29 Nov 2019 09:33:15 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:35960 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726843AbfK2OdP (ORCPT ); Fri, 29 Nov 2019 09:33:15 -0500 Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: bbrezillon) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id D7FA02923DA; Fri, 29 Nov 2019 14:33:13 +0000 (GMT) Date: Fri, 29 Nov 2019 15:33:10 +0100 From: Boris Brezillon To: Steven Price Cc: Rob Herring , Tomeu Vizoso , Alyssa Rosenzweig , stable@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH 2/8] drm/panfrost: Fix a race in panfrost_ioctl_madvise() Message-ID: <20191129153310.2f9c80e1@collabora.com> In-Reply-To: References: <20191129135908.2439529-1-boris.brezillon@collabora.com> <20191129135908.2439529-3-boris.brezillon@collabora.com> Organization: Collabora X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, 29 Nov 2019 14:24:48 +0000 Steven Price wrote: > On 29/11/2019 13:59, Boris Brezillon wrote: > > If 2 threads change the MADVISE property of the same BO in parallel we > > might end up with an shmem->madv value that's inconsistent with the > > presence of the BO in the shrinker list. > > I'm a bit worried from the point of view of user space sanity that you > observed this - but clearly the kernel should be robust! It's not something I observed, just found the race by inspecting the code, and I thought it was worth fixing it. > > > > > The easiest solution to fix that is to protect the > > drm_gem_shmem_madvise() call with the shrinker lock. > > > > Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support") > > Cc: > > Signed-off-by: Boris Brezillon > > Reviewed-by: Steven Price Thanks. > > > --- > > drivers/gpu/drm/panfrost/panfrost_drv.c | 9 ++++----- > > 1 file changed, 4 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c > > index f21bc8a7ee3a..efc0a24d1f4c 100644 > > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c > > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c > > @@ -347,20 +347,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data, > > return -ENOENT; > > } > > > > + mutex_lock(&pfdev->shrinker_lock); > > args->retained = drm_gem_shmem_madvise(gem_obj, args->madv); > > > > if (args->retained) { > > struct panfrost_gem_object *bo = to_panfrost_bo(gem_obj); > > > > - mutex_lock(&pfdev->shrinker_lock); > > - > > if (args->madv == PANFROST_MADV_DONTNEED) > > - list_add_tail(&bo->base.madv_list, &pfdev->shrinker_list); > > + list_add_tail(&bo->base.madv_list, > > + &pfdev->shrinker_list); > > else if (args->madv == PANFROST_MADV_WILLNEED) > > list_del_init(&bo->base.madv_list); > > - > > - mutex_unlock(&pfdev->shrinker_lock); > > } > > + mutex_unlock(&pfdev->shrinker_lock); > > > > drm_gem_object_put_unlocked(gem_obj); > > return 0; > > >