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 gW6D1zCO kIsq/RQ3E8nvhUEInsej2XFi2wiacNjntENt9vikNCrtR7UHcMrcAezbZYG0bIaAqKtBkLlFDBCsxvG8y5gZc7PrQQL8KIU9bvwvg1lTKxCtrKsbMUpkPBwZr0svd/Xn3xKYkp29fj8eZVoXAuMwGTwqViCg5EadjmSO8kMrai/oUlTuGaMdA7pJJnqDSUkapQYs5JSPe0H+hGBF5U8vv0Tb2tinKiTXVqC/d9Wp90YESk7F3aD3KSmHd54ZBLmrllvf4hDsAoitaEN98p0FbDfCKOkH0lwI65TUQHUwK2uaKJpQK1OFmvWuAxjLDKoMs/vdVtWUOsF85RTK7BOgZb30Noe8SGS+Ob9We1G3z7qBd7CqqjY/M84QvHfJHZJNRBrKex/fLCxaiu4001JSOXFhpaepoukd72K2wM5ZttUbTT3bMOTxdM9404034XD/JoAlP3bN933eZTfN00ojoYoP3D7fUd3XZAAcg6N1pQwQo9EY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11 Mar 2026, at 9:33, David Hildenbrand (Arm) wrote: > On 3/11/26 14:23, Usama Arif wrote: >> folio_migrate_flags() transfers folio state from source to destination= >> during migration, but does not transfer the large_rmappable flag. >> >> Migration allocators like alloc_migration_target() and >> alloc_misplaced_dst_folio() use __folio_alloc() directly without >> wrapping the result in page_rmappable_folio(), so the destination foli= o >> never gets large_rmappable set. >> >> This becomes a problem when a folio on the deferred split queue is >> migrated: the destination folio can be added to the deferred split que= ue >> via deferred_split_folio() (which does not check large_rmappable), but= >> when the folio is later freed, folio_unqueue_deferred_split() bails ou= t >> early because large_rmappable is not set: >> >> if (folio_order(folio) <=3D 1 || !folio_test_large_rmappable(folio))= >> return false; >> >> This leaves a stale entry on the deferred split queue, leading to >> use-after-free when the shrinker walks the list. >> >> Fix this by transferring large_rmappable in folio_migrate_flags(), >> consistent with how all other folio flags are handled. >> >> Fixes: dafff3f4c850 ("mm: split underused THPs") >> Signed-off-by: Usama Arif >> --- >> mm/migrate.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 3380021fd3db..ee1c7bc851dd 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -846,6 +846,9 @@ void folio_migrate_flags(struct folio *newfolio, s= truct folio *folio) >> folio_copy_owner(newfolio, folio); >> pgalloc_tag_swap(newfolio, folio); >> >> + if (folio_test_large_rmappable(folio)) >> + folio_set_large_rmappable(newfolio); >> + >> mem_cgroup_migrate(folio, newfolio); >> } >> EXPORT_SYMBOL(folio_migrate_flags); > > compaction_alloc_noprof() does the page_rmappable_folio() at the end. > > I'd assume that all migration allocation functions must take care of th= at. > > It's a responsibility of the folio allocation code, not folio migration= > code. I agree. The migration allocation function needs to give a folio or other= types of page matching the original one. Do we want to turn this into a WARN to make sure newfolio matches folio's large_rmappable state? -- Best Regards, Yan, Zi