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SubjectRe: Race in shrink_cache
Date
On Thursday 05 September 2002 08:36, Andrew Morton wrote:
> Daniel Phillips wrote:
> >
> > Hi Marcelo,
> >
> > This looks really suspicious, vmscan.c#435:
> >
> > spin_unlock(&pagemap_lru_lock);
> > if (put_page_testzero(page))
> > __free_pages_ok(page, 0);
> > /* avoid to free a locked page */
> > page_cache_get(page);
> >
> > /* whoops, double free coming */
> >
> > I suggest you bump the page count before releasing the lru lock. The race
> > shown above may not in fact be possible, but the current code is fragile.
> >
>
> That's OK. The page has a ref because of nonzero ->buffers And it
> is locked, which pins page->buffers.

Yes, true. Calm down ladies and gentlemen, and move away from the exits,
there is no fire. While we're in here, do you have any idea what this is
about:

/*
* We must not allow an anon page
* with no buffers to be visible on
* the LRU, so we unlock the page after
* taking the lru lock
*/

That is, what's scary about an anon page without buffers?

--
Daniel
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