Messages in this thread | | | Date | Tue, 17 Mar 2020 05:09:30 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCHv7 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path |
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On Tue, Mar 17, 2020 at 07:47:32PM +0800, Pingfan Liu wrote: > FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is > going to be given to hardware and can't move. It would truncate CMA > permanently and should be excluded. > > In gup slow path, slow path, where > __gup_longterm_locked->check_and_migrate_cma_pages() handles FOLL_LONGTERM, > but in fast path, there lacks such a check, which means a possible leak of > CMA page to longterm pinned. > > Place a check in try_grab_compound_head() in the fast path to fix the leak, > and if FOLL_LONGTERM happens on CMA, it will fall back to slow path to > migrate the page. > > Some note about the check: > Huge page's subpages have the same migrate type due to either > allocation from a free_list[] or alloc_contig_range() with param > MIGRATE_MOVABLE. So it is enough to check on a single subpage > by is_migrate_cma_page(subpage)
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
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