Re: [rfc 1/4] mm: Introduce may_adjust_brk helper

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Thu, Jul 24, 2014 at 07:32:25PM +0000, Serge Hallyn wrote:
> Quoting Cyrill Gorcunov (gorcunov@openvz.org):
> > To eliminate code duplication lets introduce may_adjust_brk
> > helper which we will use in brk() and prctl() syscalls.
> > 
> > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Tejun Heo <tj@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Andrew Vagin <avagin@openvz.org>
> > Cc: Eric W. Biederman <ebiederm@xmission.com>
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Serge Hallyn <serge.hallyn@canonical.com>
> > Cc: Pavel Emelyanov <xemul@parallels.com>
> > Cc: Vasiliy Kulikov <segoon@openwall.com>
> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> > Cc: Julien Tinnes <jln@google.com>
> > ---
> >  include/linux/mm.h |   14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > Index: linux-2.6.git/include/linux/mm.h
> > ===================================================================
> > --- linux-2.6.git.orig/include/linux/mm.h
> > +++ linux-2.6.git/include/linux/mm.h
> > @@ -18,6 +18,7 @@
> >  #include <linux/pfn.h>
> >  #include <linux/bit_spinlock.h>
> >  #include <linux/shrinker.h>
> > +#include <linux/resource.h>
> >  
> >  struct mempolicy;
> >  struct anon_vma;
> > @@ -1780,6 +1781,19 @@ extern struct vm_area_struct *copy_vma(s
> >  	bool *need_rmap_locks);
> >  extern void exit_mmap(struct mm_struct *);
> >  
> > +static inline int may_adjust_brk(unsigned long rlim,
> > +				 unsigned long new_brk,
> > +				 unsigned long start_brk,
> > +				 unsigned long end_data,
> > +				 unsigned long start_data)
> > +{
> > +	if (rlim < RLIMIT_DATA) {
> 
> In the code you're replacing, this was RLIM_INFINITY.  Did you really
> mean for this to be RLIMIT_DATA, aka 2?

Good catch, thanks Serge! Better would be to pass the type of resource
(as Kees suggested) here instead of @rlim itself and sure to compare
with RLIM_INFINITY.

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