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From: Linus Torvalds on 13 Aug 2010 21:00
On Fri, Aug 13, 2010 at 5:11 PM, Greg KH <gregkh(a)suse.de> wrote:
>
> That's a warning that current->mm is null. �I don't know enough about
> the mm subsystem to say if this is normal or not, and I don't at first
> glance, see how this patch could have caused this to happen.

We call that whole "expand_stack()" through handle_mm_fault(), and
that's _not_ called just for the process itself. So "current->mm" is
sometimes simply the wrong thing to use - like when you access the VM
of another process (during fork for the argument setup of the new VM,
or during ptrace etc).

Which is why I think commit 05fa199d45c should fix it. It makes the
stack expansion thing use the right mm. Which it just _happened_ to do
before, because it was always called just from the faulting code where
current->mm happened to be the right mm.

But I really don't know if there might be other issues lurking too.

Linus
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