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SubjectRe: Race in shrink_cache
Daniel Phillips wrote:
>
> ...
> /*
> * 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?

ooop. That's an akpm comment. umm, err..

It solves this BUG:

http://www.cs.helsinki.fi/linux/linux-kernel/2001-37/0594.html

Around the 2.4.10 timeframe, Andrea started putting anon pages
on the LRU. Then he backed that out, then put it in again. I
think this comment dates from the time when anon pages were
not on the LRU. So there's a little window there where the
page is unlocked, we've just dropped its swapdev buffers, the page is
on the LRU and pagemap_lru_lock is not held.

So another CPU came in, found the page on the LRU, saw that it had
no ->mapping and no ->buffers and went BUG.

The fix was to take pagemap_lru_lock before unlocking the page.

The comment is stale.
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