From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947228AbcHRNPa (ORCPT ); Thu, 18 Aug 2016 09:15:30 -0400 Received: from mail-yw0-f196.google.com ([209.85.161.196]:34928 "EHLO mail-yw0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946586AbcHRNOc (ORCPT ); Thu, 18 Aug 2016 09:14:32 -0400 MIME-Version: 1.0 In-Reply-To: <20160818130845.GB6232@phenom.ffwll.local> References: <57B44D2E.2030301@oracle.com> <20160817170827.GC2356@ZenIV.linux.org.uk> <20160817191534.GF2356@ZenIV.linux.org.uk> <20160818083651.GY6232@phenom.ffwll.local> <20160818130845.GB6232@phenom.ffwll.local> From: Rob Clark Date: Thu, 18 Aug 2016 09:14:30 -0400 Message-ID: Subject: Re: Use of copy_from_user in msm_gem_submit.c while holding a spin_lock To: Rob Clark , Al Viro , Vaishali Thakkar , David Airlie , linux-arm-msm , "dri-devel@lists.freedesktop.org" , freedreno@lists.freedesktop.org, Linux Kernel Mailing List , Julia Lawall Cc: Daniel Vetter Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 18, 2016 at 9:08 AM, Daniel Vetter wrote: > On Thu, Aug 18, 2016 at 06:55:12AM -0400, Rob Clark wrote: >> On Thu, Aug 18, 2016 at 4:36 AM, Daniel Vetter wrote: >> > On Wed, Aug 17, 2016 at 05:29:31PM -0400, Rob Clark wrote: >> >> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c >> >> index 6cd4af4..4502e4b 100644 >> >> --- a/drivers/gpu/drm/msm/msm_gem.c >> >> +++ b/drivers/gpu/drm/msm/msm_gem.c >> >> @@ -201,6 +201,13 @@ int msm_gem_fault(struct vm_area_struct *vma, >> >> struct vm_fault *vmf) >> >> pgoff_t pgoff; >> >> int ret; >> >> >> >> + /* I think this should only happen if userspace tries to pass a >> >> + * mmap'd but unfaulted gem bo vaddr into submit ioctl, triggering >> >> + * a page fault while struct_mutex is already held >> >> + */ >> >> + if (mutex_is_locked_by(&dev->struct_mutex, current)) >> >> + return VM_FAULT_SIGBUS; >> > >> > This is an ok (well still horrible) heuristics for the shrinker, but for >> > correctness it kinda doesn't cut it. What you need to do instead is drop >> > all the locks, copy relocations into a temp memory area and then proceed >> > in the msm command submission path above. >> > >> > Also reentrant mutexes are evil ;-) >> >> Please note that this is not a reentrant mutex in the fault path, it >> bails with VM_FAULT_SIGBUG! > > Except on UP it totally deadlocks ;-) except UP does not exist ;-) like I mentioned, I can add 'depends SMP' to kconfig BR, -R > -Daniel > >> There is never a legit reason to use a gem bo for the bos (or cmds) >> table in the ioctl, so while this may not be pretty, I believe it is >> an acceptable solution. > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch