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h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y0qWxXCEYRB1IYQAjN7og9sKOhPvf/8dyTcdvfDVahlt6YjdUMYvfUbO8aPrwv3VM +xydqttF/zBl1udSAxeUVhQMhyKi+cDrH7JX+bdGu4gHZ+Uv/6dKg+645sQ1GKH1wp GZroB5mqePcvfqPjRx7daRjX1XbmrRWnlWNSjbFs= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: Dev Jain , riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: [PATCH v3 1/9] mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one Date: Wed, 6 May 2026 15:14:56 +0530 Message-Id: <20260506094504.2588857-2-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260506094504.2588857-1-dev.jain@arm.com> References: <20260506094504.2588857-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 3F78040005 X-Rspam-User: X-Stat-Signature: 369bc86qpxak6cur3cwf6mywrnjpgqfo X-HE-Tag: 1778060729-290480 X-HE-Meta: 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 VI/zgiij LRSsTlm3kgbVcsVt2zR+W4Eh7QidCjiAHgepgbP8ep+0L9eD/Xnx0bOupiQY+OcjWjhPjVt4Y2jKF2AEyLlQFNmNbmYceS0aFFlMWc2b3wy8VdFDMEBwTBNKhehFNDSmqYWuhJYhRBvzv4MZL6zl1gJhakmfqTv1p7tfsL7kvS/CKTlpvYCXXxIDLHNuH6BFWiE6Be9vh5KVphQ7PAGI7s6TjtV8z9srFM46Kwil9xHvxeawa0t0oXEbt7Rd5UiAoUqtI8/T7tD2f0bCzpPRuIMhgLIndJRcccEohwJ0vD+RkByIpOreUzFIcwq1GfzmzLLuUfVQQp55gXdx8RrtouTWrDquqzt057V+t 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 Acked-by: Barry Song --- mm/rmap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index fb3c351f8c458..a5f067a09de0f 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