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authorMinchan Kim2022-05-24 10:15:25 -0700
committerakpm2022-05-27 09:33:46 -0700
commit1c563432588dbffa71e67ca6e37c826f9fa86e04 (patch)
tree429c3c09f94dbeb3857f580985b68788baa48c74 /mm
parentba6851b45d2d5b07436d8fc43451bad354dc4884 (diff)
mm: fix is_pinnable_page against a cma page
Pages in the CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA so the current is_pinnable_page() could miss CMA pages which have MIGRATE_ISOLATE. It ends up pinning CMA pages as longterm for the pin_user_pages() API so CMA allocations keep failing until the pin is released. CPU 0 CPU 1 - Task B cma_alloc alloc_contig_range pin_user_pages_fast(FOLL_LONGTERM) change pageblock as MIGRATE_ISOLATE internal_get_user_pages_fast lockless_pages_from_mm gup_pte_range try_grab_folio is_pinnable_page return true; So, pinned the page successfully. page migration failure with pinned page .. .. After 30 sec unpin_user_page(page) CMA allocation succeeded after 30 sec. The CMA allocation path protects the migration type change race using zone->lock but what GUP path need to know is just whether the page is on CMA area or not rather than exact migration type. Thus, we don't need zone->lock but just checks migration type in either of (MIGRATE_ISOLATE and MIGRATE_CMA). Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause rejecting of pinning pages on MIGRATE_ISOLATE pageblocks even though it's neither CMA nor movable zone if the page is temporarily unmovable. However, such a migration failure by unexpected temporal refcount holding is general issue, not only come from MIGRATE_ISOLATE and the MIGRATE_ISOLATE is also transient state like other temporal elevated refcount problem. Link: https://lkml.kernel.org/r/20220524171525.976723-1-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> Cc: David Hildenbrand <david@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page_alloc.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6f6e4649ac21..56b3a5d67325 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -482,8 +482,12 @@ unsigned long __get_pfnblock_flags_mask(const struct page *page,
bitidx = pfn_to_bitidx(page, pfn);
word_bitidx = bitidx / BITS_PER_LONG;
bitidx &= (BITS_PER_LONG-1);
-
- word = bitmap[word_bitidx];
+ /*
+ * This races, without locks, with set_pfnblock_flags_mask(). Ensure
+ * a consistent read of the memory array, so that results, even though
+ * racy, are not corrupted.
+ */
+ word = READ_ONCE(bitmap[word_bitidx]);
return (word >> bitidx) & mask;
}