Messages in this thread Patch in this message | | | Date | Wed, 15 Jun 2011 21:52:07 -0700 | From | Andrew Morton <> | Subject | Re: fs/exec.c: use BUILD_BUG_ON for VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP |
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On Wed, 15 Jun 2011 21:45:00 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Wed, Jun 15, 2011 at 9:35 PM, Randy Dunlap <randy.dunlap@oracle.com> 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 <mhocko@suse.cz>
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 <mhocko@suse.cz> Cc: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> ---
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; _
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