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4GbldwsLDsVkATjr+czX18uIyOug0dHM15VPP/q9uBuwmcvNSnNHHG9bfpu/c4FK7Ju/T1l+OkgOO9vMT9CE9cfmTrMqTgk4sHp4svWBcl18ptyGmBshll32OOQeSppFQgFK9Lt5EqSIbKIAJY6Y/2Q/mmknRR7ngUug1pn6Zz34nlPORx3MUGAqPJRO73kpOU1iHJGxv5u1N++Fwj2bigSKqZU5Xywl2E5NUT1TdxsD6H9zv81uGEsoRdttasSb/3sbRdDjADyrnApcIhJMah8/Joux0+zSy89r14Yfaqissqz0Rwp8pN620HKoiP8RaPNgPBRZwq9Ajh5P+uNEfX28dhkBzQngwdqHV/C/mbdv26oWQQQnjzv6GmUdVSsqqkGnLGw3H3erDGr9PW1BIQbeoeExQlQ6KjkEHO/JiV7nDQls= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu Oct 29, 2026 at 10:54 AM EDT, David Hildenbrand (Arm) wrote: > On 10/29/26 15:31, Zi Yan wrote: >> On Thu Oct 29, 2026 at 6:47 AM EDT, David Hildenbrand (Arm) wrote: >>> On 10/29/26 10:08, Barry Song wrote: >>>> >>>> I assume the race is harmless, but silencing KCSAN is still worthwhile= . >>=20 >> data_race() would work too. >>=20 >>> >>> Isn't there a way we could lose the PG_waiters flag? >>=20 >> The PG_waiters on the original folio/the original head page is not lost, > > Ah, so it's not on arbitrary tail pages, just the old head. > >> but there is a chance PG_waiters is lost in the new head, because >> prep_compound_page() uses __SetPageHead() and can ignore the atomic set >> of PG_waiters. > > Fun. > ...> >> Solutions can be: >>=20 >> 1. Use atomic SetPageHead() in prep_compound_page(). > > That sounds like the right thing to do? Yes, simpler, but the atomic op can be costly at compound page init time. My plan is to add prep_compound_page_atomic() for __split_folio_to_order() and the atomic version SetPageHead(). Fixes: c010d47f107f6 ("mm: thp: split huge page to any lower order pages"). Will send a patch soon. --=20 Best Regards, Yan, Zi