Re: Oops in __free_pages_ok (pre7-1) (Long) (backtrace)

[kanoj@google.engr.sgi.com (Kanoj Sarcar)]

> 
> 
> On Wed, 3 May 2000, Kanoj Sarcar wrote:
> > > So "is_page_shared()" can be entirely crap. And can tell shrink_mmap()
> > 
> > Not really ... look at other places that call is_page_shared, they all
> > hold the pagelock. shrink_mmap does not bother with is_page_shared logic.
> 
> That wasn't my argument.
> 
> My argument is that yes, the _callers_ of is_page_shared() all hold the
> page lock. No question about that. But the things that is_page_shared()
> actually tests can be modified without holding the page lock, so the page
> lock doesn't actually _protect_ it. See?
>

Give me an example where the page_lock is not actually protecting the
"sharedness" of the page. Note that though the page_count and swap_count
are not themselves protected by page_lock, the "sharedness" could never 
change while you have the page_lock. "Sharedness" being whatever
is_page_shared() returns. Unless you can give me an example ....

Wait a second. I was familiar with is_page_shared() having 

        if (PageSwapCache(page))
                count += swap_count(page) - 2;

and now I see it is

        if (PageSwapCache(page))
                count += swap_count(page) - 2 - !!page->buffers;

Kanoj
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