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FROMLIST: BACKPORT: mm: fix is_pinnable_page against on cma page

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Pages on CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA
so current is_pinnable_page could miss CMA pages which has MIGRATE_
ISOLATE. It ends up pinning CMA pages as longterm at pin_user_pages
APIs so CMA allocation keep failed 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.

Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>

Conflicts:
        include/linux/mm.h

1. There is no is_pinnable_page in 5.10

Link: https://lore.kernel.org/all/20220524171525.976723-1-minchan@kernel.org/
Bug: 231227007
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I5cdd2b8eefdd7e89658abd21c32aa84876ad7782
Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
This commit is contained in:
Minchan Kim 2022-05-09 10:18:31 -07:00 committed by Ksawlii
parent bc0e96e7ae
commit 33372300d9
2 changed files with 11 additions and 2 deletions
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6
include/linux/mmzone.h
View file

@ -74,7 +74,11 @@ extern const char * const migratetype_names[MIGRATE_TYPES];
#ifdef CONFIG_CMA
# define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
# define is_migrate_cma_page(_page) (get_pageblock_migratetype(_page) == MIGRATE_CMA)
# define is_migrate_cma_page(_page) ({ \
int mt = get_pageblock_migratetype(_page); \
bool ret = (mt == MIGRATE_ISOLATE || mt == MIGRATE_CMA) ? true : false; \
ret; \
})
# define get_cma_migrate_type() MIGRATE_CMA
#else
# define is_migrate_cma(migratetype) false

7
mm/page_alloc.c
View file

@ -495,7 +495,12 @@ unsigned long __get_pfnblock_flags_mask(struct page *page,
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;
}