Messages in this thread | | | Date | Tue, 15 Jun 2010 21:13:37 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH 11/12] vmscan: Write out dirty pages in batch |
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On Tue, Jun 15, 2010 at 06:53:41AM -0400, Christoph Hellwig wrote: > > + /* > > + * XXX: This is the Holy Hand Grenade of PotentiallyInvalidMapping. As > > + * the page lock has been dropped by ->writepage, that mapping could > > + * be anything > > + */ > > Why is this an XXX comment?
It's just a pretty simple use-after-free. Maybe people forget it because ->writepage is an asynchronous API.
> > + * > > + * XXX: Is there a problem with holding multiple page locks like this? > > I think there is. There's quite a few places that do hold multiple > pages locked, but they always lock pages in increasing page->inxex order. > Given that this locks basically in random order it could cause problems > for those places.
There shouldn't be a problem _holding_ the locks, but there is a problem waiting for multiple locks out of page->index order.
But there is a problem with holding the lock of a lot of pages while calling ->writepage on them. So yeah, you can't do that.
Hmm, I should rediff that lockdep page_lock patch and get it merged. (although I don't know if that can catch these all these problems easily)
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