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[92.242.248.94]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-46cf775a4f0sm13209676f8f.17.2026.06.25.14.28.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Jun 2026 14:28:23 -0700 (PDT) From: Jakov Novak To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sasha Levin , linux-kernel-mentees@lists.linux.dev, Shuah Khan , Yu Zhao , syzbot+03fd9b3f71641f0ebf2d@syzkaller.appspotmail.com, Andrew Morton , Jakov Novak Subject: [PATCH 6.1.y] mm/mglru: skip special VMAs in lru_gen_look_around() Date: Thu, 25 Jun 2026 23:27:51 +0200 Message-ID: <20260625212751.23612-1-jakovnovak30@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Yu Zhao [ Upstream commit c28ac3c7eb945fee6e20f47d576af68fdff1392a ] Special VMAs like VM_PFNMAP can contain anon pages from COW. There isn't much profit in doing lookaround on them. Besides, they can trigger the pte_special() warning in get_pte_pfn(). Skip them in lru_gen_look_around(). Link: https://lkml.kernel.org/r/20231223045647.1566043-1-yuzhao@google.com Fixes: 018ee47f1489 ("mm: multi-gen LRU: exploit locality in rmap") Signed-off-by: Yu Zhao Reported-by: syzbot+03fd9b3f71641f0ebf2d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/000000000000f9ff00060d14c256@google.com/ Cc: Signed-off-by: Andrew Morton [fix conflicts with variable declarations and vma pointer usage] Signed-off-by: Jakov Novak --- mm/vmscan.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 1f7a90ecc700..f6f8c18dc45f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4622,6 +4622,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) struct lru_gen_mm_walk *walk; int young = 0; unsigned long bitmap[BITS_TO_LONGS(MIN_LRU_BATCH)] = {}; + struct vm_area_struct *vma = pvmw->vma; struct folio *folio = pfn_folio(pvmw->pfn); struct mem_cgroup *memcg = folio_memcg(folio); struct pglist_data *pgdat = folio_pgdat(folio); @@ -4635,11 +4636,15 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) if (spin_is_contended(pvmw->ptl)) return; + /* exclude special VMAs containing anon pages from COW */ + if (vma->vm_flags & VM_SPECIAL) + return; + /* avoid taking the LRU lock under the PTL when possible */ walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL; - start = max(pvmw->address & PMD_MASK, pvmw->vma->vm_start); - end = min(pvmw->address | ~PMD_MASK, pvmw->vma->vm_end - 1) + 1; + start = max(pvmw->address & PMD_MASK, vma->vm_start); + end = min(pvmw->address | ~PMD_MASK, vma->vm_end - 1) + 1; if (end - start > MIN_LRU_BATCH * PAGE_SIZE) { if (pvmw->address - start < MIN_LRU_BATCH * PAGE_SIZE / 2) @@ -4660,7 +4665,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) for (i = 0, addr = start; addr != end; i++, addr += PAGE_SIZE) { unsigned long pfn; - pfn = get_pte_pfn(pte[i], pvmw->vma, addr); + pfn = get_pte_pfn(pte[i], vma, addr); if (pfn == -1) continue; @@ -4671,7 +4676,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) if (!folio) continue; - if (!ptep_test_and_clear_young(pvmw->vma, addr, pte + i)) + if (!ptep_test_and_clear_young(vma, addr, pte + i)) VM_WARN_ON_ONCE(true); young++; -- 2.54.0