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b=FR5L/D52LKB9zHzj8bFmrpj8prjrN+ZOoqIUYJ1ckK9mkcsmdzuGWsEb39U58Hwkm R4kBShD1Docgxseg4ptMOSQwGwW5kgq8jjIbElR2tiJPDZaFIxZ/lj26c22jto7zLY 8UlsmyZazPQAuRvhtoR5NlJ6DmO6B/sXgdwZ8ldNMyRjuN9X2IdVaVth0Elf9pgqJf OYQSjyV1V0dqEsmnldjsvXHEVBCEgC0RlRcbAcx4aaReAb2bCWlhuSBLozzW3MF77C KHEvrSICTm0HdOtMjI4E1GzVOZ4lIuALRwuB7hVb+wh0fSPpnrQXY+wHNHDwmQsYu1 Wz/WSl+rrB63w== Message-ID: <46edc7f1-f97e-4ff3-bf11-a56feb8e33b4@kernel.org> Date: Wed, 11 Mar 2026 14:33:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: migrate: transfer large_rmappable flag in folio_migrate_flags() To: Usama Arif , Andrew Morton , npache@redhat.com, ziy@nvidia.com, willy@infradead.org, linux-mm@kvack.org Cc: matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260311132342.3193160-1-usama.arif@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1528D120013 X-Stat-Signature: ja3oi5b1oswdy374njbgeyhqoude3gmr X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1773236008-298849 X-HE-Meta: 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 wcfb+1XB DNr9fwttjY3WwlG24BkawXVaxrR21qrLKIymhpMlOjNKWbDNqCHr/s/4TxnQQeBaXuFAlzhmF4yeePkmpi1hS3wcKwsF7RZC0lUDnf5oT2Avs1gPueiwCb163UNbOKZprhed62VEbQGxT9mq5W2eLC8ocDriGQtO7YteHraRCimtTLlINcn+I4JjVrvKNZ70rnqrOH617Ph6uTbdhLKyoKlwoQur9AQa7KBssGeOscjuvx6DhupNHfhc3G88c6mh+1RraoK74yphedg+3eIzvY3/4A+dK0MEWjqWAi/MJze1EoCJa1l/GCFOHnmvDq4lvlBrYEJJDz0MupkCQX6Z0RNSY5korrLTxjQzov6fFURXsmLOcUpdlWDPfFQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 folio > 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 queue > via deferred_split_folio() (which does not check large_rmappable), but > when the folio is later freed, folio_unqueue_deferred_split() bails out > early because large_rmappable is not set: > > if (folio_order(folio) <= 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, struct 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 that. It's a responsibility of the folio allocation code, not folio migration code. -- Cheers, David