David Hildenbrand <david@xxxxxxxxxx> writes: > 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) Right, I don't know of any other triggers so based on the discussion Pasha pointed me at I think the infinite loop is probably fine unless there are other bugs. Apologies I should have copied you on the new version which is just a clean-up now - https://lore.kernel.org/linux-mm/20220804032241.859891-1-apopple@xxxxxxxxxx/
