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SubjectRe: [rfc 3/3] prctl: Add PR_SET_MM codes to tune up mm_struct entires
On Wed, Dec 07, 2011 at 02:43:55PM -0800, Andrew Morton wrote:
> On Wed, 7 Dec 2011 16:27:18 +0400
> Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>
> > At process of task restoration we need a way to tune up
> > a few members of mm_struct structure such as start_code,
> > end_code, start_data, end_data, start_stack, start_brk, brk.
>
> I don't really know what "tune up" means in this context. Can we
> please be more specific and detailed here? It appears that the patch
> permits userspace to directly modify these fields.
>

ok

>
> The prctl(2) manpage will need to be updated. Please Cc Michael on all
> such changes.
>

you mean -- Michael Kerrisk, mtk AT man7.org, right?

...
> > +
> > + mm = get_task_mm(current);
>
> Is it necessaary to run the expensive get_task_mm() for `current'?
> `current' is known to be running and you have control of it here -
> nobody will be taking our mm away. Simply use current->mm? The
> function actually uses current->mm later on in several places.

hmm, indeed, i'll update, thanks!

>
> > + if (!mm)
> > + return -ENOENT;
> > +
> > + down_read(&mm->mmap_sem);
> > + vma = find_vma(mm, addr);
> > +
> > + if (opt != PR_SET_MM_START_BRK &&
> > + opt != PR_SET_MM_BRK) {
>
> 80 columns, not 40 :)
>
> > + /* It must be existing VMA */
> > + if (!vma || vma->vm_start > addr)
> > + goto out;
> > + }
> > +
> > + error = -EINVAL;
> > + switch (opt) {
> > + case PR_SET_MM_START_CODE:
> > + case PR_SET_MM_END_CODE:
> > +
>
> You're adding unneeded and unconventional newlines after the `case'
> statements.
>

no, I added them by a purpose -- it's a way easier to read these
assignments, but fine -- I'll drop this nits.

>
> This is starting to add a non-trivial amount of code. Perhaps we need
> to introduce a Kconfig variable to control such things as this, to
> prevent bloating up kernels which aren't require to support c/r?
>

Dunno, Andrew. Actually I agreed that these snippets are mostly
needed for c/r only, but the initial idea over all changes was
to add levers into kernel which might be helpful not only
for c/r but for someone else as well.

Cyrill


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