Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 21 Dec 2023 04:16:34 +0000 | From | Matthew Wilcox <> | Subject | Re: [RFC 0/3] iommu/intel: Free empty page tables on unmaps |
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On Thu, Dec 21, 2023 at 03:19:12AM +0000, Pasha Tatashin wrote: > This series frees empty page tables on unmaps. It intends to be a > low overhead feature. > > The read-writer lock is used to synchronize page table, but most of > time the lock is held is reader. It is held as a writer for short > period of time when unmapping a page that is bigger than the current > iova request. For all other cases this lock is read-only. > > page->refcount is used in order to track number of entries at each page > table.
Have I not put enough DANGER signs up around the page refcount?
* If you want to use the refcount field, it must be used in such a way * that other CPUs temporarily incrementing and then decrementing the * refcount does not cause problems. On receiving the page from * alloc_pages(), the refcount will be positive.
You can't use refcount for your purpose, and honestly I'm shocked you haven't seen any of your WARNings trigger.
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