Messages in this thread Patch in this message | | | From | Pingfan Liu <> | Subject | [PATCHv6 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path | Date | Mon, 16 Mar 2020 12:34:03 +0800 |
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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; + + /* * When pinning a compound page of order > 1 (which is what * hpage_pincount_available() checks for), use an exact count to * track it, via hpage_pincount_add/_sub(). -- 2.7.5
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