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.
