Re: Can get_user_pages( ,write=1, force=1, ) result in a read-only pte and _count=2?

[Robin Holt <holt@sgi.com>]

On Thu, Jun 19, 2008 at 12:09:15PM +0100, Hugh Dickins wrote:
> On Thu, 19 Jun 2008, Nick Piggin wrote:
> > On Thursday 19 June 2008 05:01, Hugh Dickins wrote:
> > > On Thu, 19 Jun 2008, Nick Piggin wrote:

> > We're talking about swap pages, as in do_swap_page? Then AFAIKS it
> > is only the mapcount that is taken into account, and get_user_pages
> > will first break COW, but that should set mapcount back to 1, in
> > which case the userspace access should notice that in do_swap_page
> > and prevent the 2nd COW from happening.
> 
> (I assume Robin is not forking, we do know that causes this kind
> of problem, but he didn't mention any forking so I assume not.)

There has been a fork long before this mapping was created.  There was a
hole at this location and the mapping gets established and pages populated
following all ranks of the MPI job getting initialized.

Thanks,
Robin

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>