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 ONuQY6J1 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wrote: > OK have dug into this some more with a drgn script to read actual kernel > metadata state and it's simpler than I thought - the root anon_vma is > self-childed, but descendent anon_vma's are not. > > We can correct this with a anon_vma->root == anon_vma check. I believe > we're probably safe with anon_vma reuse, because in that instance the > anon_vma would not be mapped a shared folio. > > However, to be safe, I will check this, and I as I said previously, I will > add a number of tests explicitly tested forking scenarios. > > The respin should have this fully addressed. > > Thanks, Lorenzo Note that in practice, this wouldn't have broken anything, as in this case you would _have_ to have parent anon_vma's. The root will hang around even if all VMA's unmapped also, we only clear down anon_vma's once no references from the anon_vma exist, and by nature everything below the root must reference it. But the function is misleading as-is so needs fixing. As for anon_vma re-use - this is not permitted for root anon_vma's so naturally it requires a parented anon_vma, which again implies AVC's which the uncowed parent check would pick up. Additionally, the reuse implies that the folio is not mapped within the process that first created the anon_vma, and thus the num_children counts remain correct across the board. See https://pastebin.com/raw/q6wzUMLi for a detailed diagram of both scenarios with anon_vma parameters and linking derived from real-world kernel values obtained via drgn. These will form part of the added tests. Cheers, Lorenzo