On Mon, Feb 8, 2010 at 2:05 PM, KOSAKI Motohiro
[off-list ref] wrote:

quoted

--- linux-2.6-ozlabs.orig/fs/exec.c
+++ linux-2.6-ozlabs/fs/exec.c

@@ -627,10 +627,13 @@ int setup_arg_pages(struct linux_binprm

=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =

=C2=A0 goto out_unlock;

quoted

=C2=A0 =C2=A0 =C2=A0 }

+ =C2=A0 =C2=A0 stack_base =3D min(EXTRA_STACK_VM_PAGES * PAGE_SIZE,
+ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =

=C2=A0current->signal->rlim[RLIMIT_STACK].rlim_cur -

quoted

+ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =

=C2=A0 =C2=A0PAGE_SIZE);

This line is a bit unclear why "- PAGE_SIZE" is necessary.
personally, I like following likes explicit comments.

=C2=A0 =C2=A0 =C2=A0 =C2=A0stack_expand =3D EXTRA_STACK_VM_PAGES * PAGE_S=

IZE;

=C2=A0 =C2=A0 =C2=A0 =C2=A0stack_lim =3D ACCESS_ONCE(rlim[RLIMIT_STACK].r=

lim_cur);

=C2=A0 =C2=A0 =C2=A0 =C2=A0/* Initial stack must not cause stack overflow=

. */

=C2=A0 =C2=A0 =C2=A0 =C2=A0if (stack_expand + PAGE_SIZE > stack_lim)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0stack_expand =3D s=

tack_lim - PAGE_SIZE;

note: accessing rlim_cur require ACCESS_ONCE.


Thought?

It's better to use the helper function: rlimit().