33372300d9
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>
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