Messages in this thread | | | Date | Mon, 16 Mar 2020 01:55:36 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCHv6 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path |
| |
On Mon, Mar 16, 2020 at 12:34:03PM +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) > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > Cc: Ira Weiny <ira.weiny@intel.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Mike Rapoport <rppt@linux.ibm.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: John Hubbard <jhubbard@nvidia.com> > Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Shuah Khan <shuah@kernel.org> > Cc: Jason Gunthorpe <jgg@ziepe.ca> > To: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/gup.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 9df77b1..78132cf 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -89,6 +89,15 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, > int orig_refs = refs; > > /* > + * 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 subpage. > + */ > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) > + return NULL;
Wrong indentation. We either align two tabs for continuation statements, or after the opening brace of the previous line. With a likely or unlikely thrown in the former IMHO looks much better. E.g.
if (unlikely(flags & FOLL_LONGTERM) && is_migrate_cma_page(page)) return NULL;
| |