Re: changing mm->mmap_sem (was: Re: system call for process information?)

From: Stephen C. Tweedie (sct@redhat.com)
Date: Mon Mar 19 2001 - 07:54:51 EST


Hi,

On Sun, Mar 18, 2001 at 10:34:38AM +0100, Manfred Spraul wrote:

> > The problem is that mmap_sem seems to be protecting the list
> > of VMAs, so taking _only_ the page_table_lock could let a VMA
> > change under us while a page fault is underway ...
>
> No, that can't happen.

It can. Page faults often need to block, so they have to be able to
drop the page_table_lock. Holding the mmap_sem is all that keeps the
vma intact until the IO is complete.

Cheers,
 Stephen
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