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bh=b08HICgezPVD7gUzyQf2pI1dALNHj0lOGqN3C5nNR0Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UXc3vPoCgwsQbgN+hDlEu3IRjHexFrPZmZsCCe4+iKS7P2XZFV6VtHkFHXQ6E0Ubr 1FEXUb/fAwuvXn/4Yq7VI3p4t9ki5EU1Jl953XMq83vVMouhMrLnLJsM7YJR3IDaEt VkOcTq+8HOT3JjA5js+iX624XwvwQwLxVI0HBGd4= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, hughd@google.com, chrisl@kernel.org Cc: ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, riel@surriel.com, harry@kernel.org, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, Dev Jain Subject: [PATCH v2 1/9] mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one Date: Fri, 10 Apr 2026 16:01:56 +0530 Message-Id: <20260410103204.120409-2-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260410103204.120409-1-dev.jain@arm.com> References: <20260410103204.120409-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 89FC7A0014 X-Stat-Signature: jc4dgw76cddmkr41aw9nutd6jhq975ou X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1775817150-639429 X-HE-Meta: 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 56uvNcd+ xfukcIwGzylcRJFmzCIAifWy1cj4Y3uLGqTOuivQBDFlsqiUcvm0/RITB4HLZaZt1BFy6ZUid88NaqFTbhqwc+jq3044bYUZYGNZinM1feixXxlWx0E+kvRvdzQULo/AzewFpfevEQv1Gr/K1p3Add/0z/IBwn4oIBY4wIWs4fG7zHyvWQsmrne6lUhx0keXz/s+9aXtnD5XlHJxxUJQt0p3r8kTeGJCoIqWA0BnX2qdH0L9AD1ixfU5VUpf9HZmGL/K6gYXVRFaLSer2EhJP40SYIPHw3sSkmsTv3Q0k0+CH18mcqTQS0Zx/7TtAAinK1uQPZlOdHUBgSyQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Initialize nr_pages to 1 at the start of each loop iteration, like folio_referenced_one() does. Without this, nr_pages computed by a previous folio_unmap_pte_batch() call can be reused on a later iteration that does not run folio_unmap_pte_batch() again. I don’t think this is causing a bug today, but it is fragile. A real bug would require this sequence within the same try_to_unmap_one() call: 1. Hit the pte_present(pteval) branch and set nr_pages > 1. 2. Later hit the else branch and do pte_clear() for device-exclusive PTE, and execute rest of the code with nr_pages > 1. Executing the above would imply a lazyfree folio is mapped by a mix of present PTEs and device-exclusive PTEs. In practice, device-exclusive PTEs imply a GUP pin on the folio, and lazyfree unmapping aborts try_to_unmap_one() when it detects that condition. So today this likely does not manifest, but initializing nr_pages per-iteration is still the correct and safer behavior. Signed-off-by: Dev Jain --- mm/rmap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index 78b7fb5f367ce..62a8c912fd788 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1991,7 +1991,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, struct page *subpage; struct mmu_notifier_range range; enum ttu_flags flags = (enum ttu_flags)(long)arg; - unsigned long nr_pages = 1, end_addr; + unsigned long nr_pages; + unsigned long end_addr; unsigned long pfn; unsigned long hsz = 0; int ptes = 0; @@ -2030,6 +2031,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, mmu_notifier_invalidate_range_start(&range); while (page_vma_mapped_walk(&pvmw)) { + nr_pages = 1; /* * If the folio is in an mlock()d vma, we must not swap it out. */ -- 2.34.1