On Thu, Jan 12, 2023 at 4:10 PM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > On Thu, Jan 12, 2023 at 10:12:53AM -0800, Yang Shi wrote: > > > This is totally wrong direction. Or I don't understand the race. > > > > > > At this point we already paid nearly all price of of pagetable retraction. > > > I don't see any correctness reason to stop here, except for the assert. > > > > Isn't it possible that collapse_and_free_pmd() clear the pmd which may > > point to a PTE which maps the COW'ed anon page if this race happens? > > No. At this point we have huge page in the place in the page cache and it > is locked. COW fault would serialize on the page lock. Aha, yeah, I missed the page lock. So IIUC even though anon_vma is set there should be not any COW'ed anon pages since cow fault would be blocked by the page lock. If so I tend to agree with you the lockdep assert seems unnecessary. > > -- > Kiryl Shutsemau / Kirill A. Shutemov
