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K5Td1kbQHtDDcAOY7rynTvMSMPR+3dRfjNX/iEaoCLI7h9JdrksC+5jArhIvk59aJ5J9dbKwlv3NanI7XXZAAddYHTs7nSNfUaU7Bh8CvVogrM8nvlSVyUkp4SVo5x2Qmd3a0MY26l08gQzMoHi6/PV2bEi/beVCkVb6vY7DUk04/hMfNTQ2/rcX5HROdoPwFE94hv2vHsv5rYKmDHa5XpyUixkc3zJMydNrsyqRsHXYkPv4lLdXLp1f6hrq4w6MCuRUy/nGM8DeywAWnpqE0ev8N5MXtg6d4bULSHDpPkMfPUxZ91akW+NJAFjqMBchB4nW/1thWrK5cG9IpKkQ6tZ8P1z5yNrmdKytXHKw8RSbFej/XGQyXwfMi1LEF8k8hJSpDlCmtsMEHsOEoGj3rcEdJ+p3iG5lmY9n4xDYYcN8xqZMdfg4Jfa2Fkaoj32+jkXlQCwkYYiYyoHlWHlVQQrNfhIPN1ow5eaavlHkmBVJHeBW2bQawOw3taw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri Oct 9, 2026 at 9:12 PM EDT, Lance Yang wrote: > > > On 2026/10/10 04:44, David Hildenbrand (Arm) wrote: >> On 10/9/26 22:27, Zi Yan wrote: >>> On 9 Oct 2026, at 16:23, David Hildenbrand (Arm) wrote: >>> >>>> On 10/9/26 20:17, Zi Yan wrote: >>>>> >>>>> There are some gaps we need to close before getting this fix in: >>>>> >>>>> 1. GUP-fast cannot follow the invalidated PMD: riscv and LoongArch ne= ed >>>>> pmd_access_permitted() that requires _PAGE_PRESENT; s390's >>>>> pmdp_invalidate() needs a change. >>>> >>>> Ugh. We really need pmdp_invalidate() to have reasonable semantics. Th= is whole >>>> PMD locking is a mess :( >>>> >>>>> >>>>> 2. sparc64's thp_pte_count can be imbalanced with this change (based = on >>>>> Lance's offlist feedback). >>>> >>>> Ack. >>>> >>>>> >>>>> In addition, powerpc has a page table check issue similr to riscv, wh= ere riscv >>>>> fixed it with commit 9f4a88b8d01a6. This is not related to this issue >>>>> but discovered along with the investigation. >>>> >>>> Zi, do you have the capacity to take over this patch? >>> >>> Yes, I can take over it. My plan is to send a series including >>> patches for 1 and this patch as is. powerpc fix can be a separate one. >>> >>> Best Regards, >>> Yan, Zi >>=20 >> If we need a quick stable fix we could temporarily disable the whole thi= ng until >> it is fixed, just a thought. > > +1 we could do that for now. A quick fix with minimal churn (correctness= =20 > comes first). How about the patch below? unmap_huge_pmd_locked() and __discard_anon_folio_pmd_locked() will be dead code to keep the patch small. Later, with arch fixes, the function can be re-enabled. >From 2204b9d08530796847a586428b1f782b987d071c Mon Sep 17 00:00:00 2001 From: Zi Yan Date: Fri, 9 Oct 2026 21:28:10 -0400 Subject: [PATCH] mm/rmap: don't discard lazyfree THPs at PMD level __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_fol= io_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 --- 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, st= ruct vm_area_struct *vma, } =20 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 --=20 2.53.0 --=20 Best Regards, Yan, Zi