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mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path 

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, 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Cc: Ira Weiny <ira.weiny@intel.com>
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>
Link: http://lkml.kernel.org/r/1584876733-17405-3-git-send-email-kernelfans@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Pingfan Liu 2020-04-01 21:06:04 -07:00 committed by Linus Torvalds
parent 4628b063d2
commit df3a0a21b6
1 changed files with 8 additions and 0 deletions
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8
mm/gup.c
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@ -88,6 +88,14 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page,
else if (flags & FOLL_PIN) {
int orig_refs = refs;
/*
* Can't do FOLL_LONGTERM + FOLL_PIN with CMA in the gup fast
* path, so fail and let the caller fall back to the slow path.
*/
if (unlikely(flags & FOLL_LONGTERM) &&
is_migrate_cma_page(page))
return NULL;
/*
* When pinning a compound page of order > 1 (which is what
* hpage_pincount_available() checks for), use an exact count to