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 4AKCmqCX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --=_MailMate_6E60A512-3AEE-40E7-B374-00D5534116C8_= Content-Type: text/plain On 27 Oct 2024, at 15:59, Hugh Dickins wrote: > Recent changes are putting more pressure on THP deferred split queues: > under load revealing long-standing races, causing list_del corruptions, > "Bad page state"s and worse (I keep BUGs in both of those, so usually > don't get to see how badly they end up without). The relevant recent > changes being 6.8's mTHP, 6.10's mTHP swapout, and 6.12's mTHP swapin, > improved swap allocation, and underused THP splitting. > > The new unlocked list_del_init() in deferred_split_scan() is buggy. > I gave bad advice, it looks plausible since that's a local on-stack > list, but the fact is that it can race with a third party freeing or > migrating the preceding folio (properly unqueueing it with refcount 0 > while holding split_queue_lock), thereby corrupting the list linkage. > > The obvious answer would be to take split_queue_lock there: but it has > a long history of contention, so I'm reluctant to add to that. Instead, > make sure that there is always one safe (raised refcount) folio before, > by delaying its folio_put(). (And of course I was wrong to suggest > updating split_queue_len without the lock: leave that until the splice.) > > And remove two over-eager partially_mapped checks, restoring those tests > to how they were before: if uncharge_folio() or free_tail_page_prepare() > finds _deferred_list non-empty, it's in trouble whether or not that folio > is partially_mapped (and the flag was already cleared in the latter case). > > Fixes: dafff3f4c850 ("mm: split underused THPs") > Signed-off-by: Hugh Dickins > Acked-by: Usama Arif > Reviewed-by: David Hildenbrand > Reviewed-by: Baolin Wang > --- > Based on 6.12-rc4 > v2: added ack and reviewed-bys Acked-by: Zi Yan -- Best Regards, Yan, Zi --=_MailMate_6E60A512-3AEE-40E7-B374-00D5534116C8_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEE6rR4j8RuQ2XmaZol4n+egRQHKFQFAmcenTcPHHppeUBudmlk aWEuY29tAAoJEOJ/noEUByhU0iEQAJLlS1uAn0hOGOqkULFLrlkToTq9AXpu3xl5 znXaXG9+gZrQoTeryAtY8RniHECkjxevyeETMgO1MFbGcbtnauTbC6WVCI8UgiY8 D/jFEFyh4kA12xW748ywiJqGDqxU59Ckg8YRJtZ8W0qJhyjp0RqQDtSr1Wc6jLnW 9/scGFQeh5BYw6A/f9QQc+VKJcDs8uqLKzE09mPs5NY803N3N7nWQDxO+vGD7YmY X8TncmWog7TzrxsgKCep5yykBZ/A8hRJLdLFFZ1fh2hkjSFlmzaklnfZZOyqyYtR ek0+FgHYYD9wEoKqmxaolVCTZF6fcPkZ9lBDAp3zI3ipg63A/svR5yfW6tOpIkmm P9ZkzmzkThI0porIZcPeK9t3J1qHn9wj8h66KvKB2lIZvQTRTJG/hVBoPzmmxC7g PV5gowEcGRNL2nr/5CblqQNkwDcnOSV8aSpK1iWAECiHnpURbVKlP4EBORiiLMnW YuBFVpd2Y6Y66xs9i0Vq+lkdtWms28c9vRrhud/FlkA/Dmbiwg2mD9m5Wk8efntG xkeBQPPvz/T2UCKnBwQoM8a+KBGvM4gD0tCWRsUBenmYTW5gKG1aH4YApsn47wZ/ BgTgaHAd5ykSAtWte/TJ5OovXe/emB/DXMadCEdqwAaaPZ/Y3vED2WvF85Jln3hM Trbcp6h/ =pWW1 -----END PGP SIGNATURE----- --=_MailMate_6E60A512-3AEE-40E7-B374-00D5534116C8_=--