On 04.08.22 02:12, Alistair Popple wrote: > > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > >> On Tue, 2 Aug 2022 10:30:12 +1000 Alistair Popple <apopple@xxxxxxxxxx> wrote: >> >>> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() >>> is called to migrate pages out of zones which should not contain any >>> longterm pinned pages. >>> >>> When migration succeeds all pages will have been unpinned so pinning >>> needs to be retried. This is indicated by returning zero. When all pages >>> are in the correct zone the number of pinned pages is returned. >>> >>> However migration can also fail, in which case pages are unpinned and >>> -ENOMEM is returned. However if the failure was due to not being unable >>> to isolate a page zero is returned. This leads to indefinite looping in >>> __gup_longterm_locked(). >>> >>> Fix this by simplifying the return codes such that zero indicates all >>> pages were successfully pinned in the correct zone while errors indicate >>> either pages were migrated and pinning should be retried or that >>> migration has failed and therefore the pinning operation should fail. >>> >>> This fixes the indefinite looping on page isolation failure by failing >>> the pin operation instead of retrying indefinitely. >>> >> >> Are we able to identify a Fixes: for this? Presumably something in the >> series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"? > > It seems the infinite loop was desired behaviour so I will re-spin this > as a pure clean-up. > How can the infinite loop trigger when we allow longterm-pinning the shared zeropage? (note: disallowing that for now was a bug) -- Thanks, David / dhildenb
