Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751599Ab1FPEwV (ORCPT ); Thu, 16 Jun 2011 00:52:21 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:40365 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750829Ab1FPEwU (ORCPT ); Thu, 16 Jun 2011 00:52:20 -0400 Date: Wed, 15 Jun 2011 21:52:07 -0700 From: Andrew Morton To: Linus Torvalds Cc: Randy Dunlap , Linux Kernel Mailing List , Michal Hocko , Richard Weinberger Subject: Re: fs/exec.c: use BUILD_BUG_ON for VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP Message-Id: <20110615215207.ba7a0386.akpm@linux-foundation.org> In-Reply-To: References: <201106160359.p5G3x3j4020081@hera.kernel.org> <20110615213549.9b399976.randy.dunlap@oracle.com> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2406 Lines: 66 On Wed, 15 Jun 2011 21:45:00 -0700 Linus Torvalds wrote: > On Wed, Jun 15, 2011 at 9:35 PM, Randy Dunlap wrote: > > > > fwiw, I just reported that this causes a build error in UML on x86_64 > > in mmotm-2011-06-15: > > Gaah. That sounds really familiar. Have we done this same mistake once > before already, or is it just deja-vu for some other reason. > > On x86-64 UML, we have > > #define VM_STACK_DEFAULT_FLAGS vm_stack_flags > > so VM_STACK_FLAGS ends up not being a constant, even though it really > looks like one. > > UML is _really_ confused in this area, btw. It seems to re-define that > thing if TIF_IA32 is defined. That's some crazy stuff. Doesn't the > compiler warn about it? > > I guess I should just revert that commit, though. Even if it does seem > to be the case that UML is just being crazy. Andrew? > Sure, it was just a tiny optimization. We can bring it back if Richard feels like decrazyifying UML ;) From: Michal Hocko a8bef8ff ("mm: migration: avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks") introduced a BUG_ON() to ensure that VM_STACK_FLAGS and VM_STACK_INCOMPLETE_SETUP do not overlap. The check is a compile time one, so BUILD_BUG_ON is more appropriate. Signed-off-by: Michal Hocko Cc: Mel Gorman Signed-off-by: Andrew Morton --- fs/exec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN fs/exec.c~fs-execc-use-build_bug_on-for-vm_stack_flags-vm_stack_incomplete_setup fs/exec.c --- a/fs/exec.c~fs-execc-use-build_bug_on-for-vm_stack_flags-vm_stack_incomplete_setup +++ a/fs/exec.c @@ -277,7 +277,7 @@ static int __bprm_mm_init(struct linux_b * use STACK_TOP because that can depend on attributes which aren't * configured yet. */ - BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP); + BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP); vma->vm_end = STACK_TOP_MAX; vma->vm_start = vma->vm_end - PAGE_SIZE; vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP; _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/