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Date: Thu, 24 Jul 2014 23:21:52 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [rfc 1/4] mm: Introduce may_adjust_brk helper
Message-ID: <20140724192152.GC17876@moon>
References: <20140724164657.452106845@openvz.org>
 <20140724165047.437075575@openvz.org>
 <CAGXu5j+QHcrYjT8F9TZLA8YbJzZed28scp2y22QNO20sRF8Ndw@mail.gmail.com>
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To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Andrew Vagin <avagin@openvz.org>, "Eric W. Biederman" <ebiederm@xmission.com>, "H. Peter Anvin" <hpa@zytor.com>, Serge Hallyn <serge.hallyn@canonical.com>, Pavel Emelyanov <xemul@parallels.com>, Vasiliy Kulikov <segoon@openwall.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Michael Kerrisk-manpages <mtk.manpages@gmail.com>, Julien Tinnes <jln@google.com>

On Thu, Jul 24, 2014 at 12:18:56PM -0700, Kees Cook wrote:
> >
> > +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) {
> 
> Won't rlim always be the value from a call to rlimit(RLIMIT_DATA)? Is
> there a good reason to not just put the rlimit() call in
> may_adjust_brk()? This would actually be an optimization in the
> prctl_set_mm case, since now it calls rlimit() unconditionally, but
> doesn't need to.

Nope, we use it for rlimit(RLIMIT_STACK) when checking for
@start_stack member.

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