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    SubjectRe: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs
    On Tue, 26 Jun 2012, Glauber Costa wrote:

    > > > diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
    > > > index ccc1899..914ec07 100644
    > > > --- a/include/linux/thread_info.h
    > > > +++ b/include/linux/thread_info.h
    > > > @@ -61,6 +61,12 @@ extern long do_no_restart_syscall(struct restart_block
    > > > *parm);
    > > > # define THREADINFO_GFP (GFP_KERNEL | __GFP_NOTRACK)
    > > > #endif
    > > >
    > > > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
    > > > +# define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
    > > > +#else
    > > > +# define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP)
    > > > +#endif
    > > > +
    > >
    > > This type of requirement is going to become nasty very quickly if nobody
    > > can use __GFP_KMEMCG without testing for CONFIG_CGROUP_MEM_RES_CTLR_KMEM.
    > > Perhaps define __GFP_KMEMCG to be 0x0 if it's not enabled, similar to how
    > > kmemcheck does?
    > >
    > That is what I've done in my first version of this patch. At that time,
    > Christoph wanted it to be this way so we would make sure it would never be
    > used with #CONFIG_CGROUP_MEM_RES_CTLR_KMEM defined. A value of zero will
    > generate no errors. Undefined value will.
    >
    > Now, if you ask me, I personally prefer following what kmemcheck does here...
    >

    Right, because I'm sure that __GFP_KMEMCG will be used in additional
    places outside of this patchset and it will be a shame if we have to
    always add #ifdef's. I see no reason why we would care if __GFP_KMEMCG
    was used when CONFIG_CGROUP_MEM_RES_CTLR_KMEM=n with the semantics that it
    as in this patchset. It's much cleaner by making it 0x0 when disabled.


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