On Wed, Feb 15, 2023 at 09:17:31PM -0800, Suren Baghdasaryan wrote: > Decisions about whether VMAs can be merged, split or expanded must be > made while VMAs are protected from the changes which can affect that > decision. For example, merge_vma uses vma->anon_vma in its decision Did you mean vma_merge()? > whether the VMA can be merged. Meanwhile, page fault handler changes > vma->anon_vma during COW operation. > Write-lock all VMAs which might be affected by a merge or split operation > before making decision how such operations should be performed. > It doesn't make sense (to me) to update vma->anon_vma during COW fault. AFAIK children's vma->anon_vma is allocated during fork() and page->anon_vma is updated on COW to reduce rmap walking because it's now unshared, no? As patch 26 just falls back to mmap_lock if no anon_vma is set, I think we can assume nothing updates vma->anon_vma (and its interval tree) if we are holding mmap_lock in write mode. Or am I missing something? -- Regards, Hyeonggon
