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Fri, 09 Oct 2026 19:14:27 -0700 (PDT) Received: from com-75606 ([199.47.143.7]) by smtp.gmail.com with ESMTPSA id 5614622812f47-50c0c5fe916sm4211994b6e.1.2026.10.09.19.14.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2026 19:14:27 -0700 (PDT) Date: Fri, 9 Oct 2026 19:14:22 -0700 From: Kyle Zeng To: Zi Yan Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Rik van Riel , "Liam R. Howlett" , Vlastimil Babka , Harry Yoo , Jann Horn , Lance Yang , stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/rmap: don't discard lazyfree THPs at PMD level Message-ID: References: <20261009-lazyfree-stable-fix-v1-1-70997958ef8d@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261009-lazyfree-stable-fix-v1-1-70997958ef8d@nvidia.com> X-Stat-Signature: f1b4exxqgpdf9mau9shh7r85uqjjfz9o X-Rspam-User: X-Rspamd-Queue-Id: 2E5F6A0002 X-Rspamd-Server: rspam08 X-HE-Tag: 1791598469-57119 X-HE-Meta: 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 S0eizFoO 3jfJJHPTd+McqE6t2fLXdvvU7nO0N7Ehs8zrODyApge/oM0sssk8zcoO5Bb2Y6mQqMR9Omio2dfAOxW4orrcvPw9IhS5SGGgpobFgCZZPNVxPmDFcVRIti/DQZqYzcTHlp+iE2t5yOoeS6nHq50qZow6P8wLs9P36b0Lid/luk0+W2mUzSgW3RG3DL+f6jjJ+ldsomoHYJmeK8rEh0V59d3SuXo9UKKH8PRbGzTaepDsdps47gtdv9pgzs6Krcaa96BX2exqh5gxQ48IY/1Km99nwlnZd8lKniJHj4+celqNWigh8JULKXpCwJfzZRHT2sLWSpZmngI7DZgZhX3QWHhcIwM0QDBqR5WaY1SHpPWwDdCmqc6i+6Z42AWDuS1JL2s+9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Oct 09, 2026 at 10:08:18PM -0400, Zi Yan wrote: > __discard_anon_folio_pmd_locked() clears a lazyfree THP PMD before it knows > whether the folio can be discarded, and restores it if the folio was > redirtied or has extra references. A concurrent munmap() or > MREMAP_DONTUNMAP skips the temporary none PMD and unlinks the VMA from its > anon_vma, so the folio stays mapped after the anon_vma is freed and a later > rmap walk uses the freed anon_vma. > > Using an invalidated PMD instead of a cleared one requires additional arch > code fixes. Instead, disable the PMD level discard of lazyfree THPs, as > before commit 735ecdfaf4e8 ("mm/vmscan: avoid split lazyfree THP during > shrink_folio_list()"). > > Fixes: 735ecdfaf4e8 ("mm/vmscan: avoid split lazyfree THP during shrink_folio_list()") > Reported-by: Kyle Zeng > Closes: https://lore.kernel.org/r/20261009165214.40212-2-kylebot@openai.com > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Zi Yan > --- > The proposed fix[1] requires additional arch code fixes[2]. Disable it > first for stable fix. The function will be re-enabled along with arch code > fixes. > > Link: https://lore.kernel.org/all/20261009165214.40212-2-kylebot@openai.com/ [1] > Link: https://lore.kernel.org/all/DM0II2QHWWS1.2RXEJXC8S0101@nvidia.com/ [2] > --- > mm/rmap.c | 11 ----------- > 1 file changed, 11 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 805db93fe0428..1131b76bbbc28 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2275,17 +2275,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte) { > - if (folio_test_lazyfree(folio)) { > - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) > - goto walk_done; > - /* > - * unmap_huge_pmd_locked has either already marked > - * the folio as swap-backed or decided to retain it > - * due to GUP or speculative references. > - */ > - goto walk_abort; > - } > - > if (flags & TTU_SPLIT_HUGE_PMD) { > /* > * We temporarily have to drop the PTL and > > --- > base-commit: 8b38ed9ab5b09c8ba168cbcc49524e9b380ee5c4 > change-id: 20261009-lazyfree-stable-fix-67712b2049dd > > Best regards, > -- > Yan, Zi > Reviewed-by: Kyle Zeng