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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko References: <20260415-ecc_panic-v4-0-2d0277f8f601@debian.org> <20260415-ecc_panic-v4-2-2d0277f8f601@debian.org> <6b505601-747a-0812-7544-63a8ab3cffce@huawei.com> From: Miaohe Lin Message-ID: <5e05384e-740e-b374-2370-01f96d1dac9f@huawei.com> Date: Mon, 27 Apr 2026 10:44:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.124.160] X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To kwepemq500010.china.huawei.com (7.202.194.235) X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 000891A0007 X-Stat-Signature: g8fre95p7m84ker9t1nyqamhnzjuz73d X-Rspam-User: X-HE-Tag: 1777257901-184969 X-HE-Meta: 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 vsVBMAk9 9eCXMPm4PtVGoehhaLuPDKPpEK+Q+/noGG7l/G0o0gndJewjwBgP+EuIEAnf7pSvjyEFZ+t6pAgCGLXaIIQY8X4WzwpZ75AE5JP796P17jXvKwgr0CkdIz0OmLGsSjLjyqKmDqsTzT8j5XDRheG3EcYgNHF1HD1NHdtSWGFrLi6z6smFLT1vkmir87a/episqLugfrLU5P15d0LhaDoDCDC/PiS1J6qM91Eb76HqVgODEaS5v9yOBbuGkeTBaLiUiNF/jh19rRNTDwHukhqLjdJiNCxeuzYjWx4kcG1+U+ogvWZUoIDcWFO9HBmsxoW2UmniFBO5DhYKntvHYg8nuhUbqFf+8y0Zho1WckaknXZnB0wucy0cKnyXb8w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/4/24 20:01, Breno Leitao wrote: > On Thu, Apr 23, 2026 at 10:38:19AM +0800, Miaohe Lin wrote: >>> are you suggesting I drop MF_MSG_KERNEL_HIGH_ORDER from here, or, document this >>> will not hit userspace pages? >> >> No, maybe we should rule out or document above rare case if I'm not miss something. > > Good catch. A buddy page being concurrently allocated to userspace can > briefly satisfy get_hwpoison_page() == 0 && !is_free_buddy_page(), and > that page is recoverable via the standard SIGBUS path — panicking on > it would be wrong. > > The page allocator can't filter it out either. > > check_new_pages() is gated by is_check_pages_enabled() and is a no-op > when CONFIG_DEBUG_VM=n. > > For v6 I'll try to rule out the race inside panic_on_unrecoverable_mf() so > action_result() stays unchanged: > > case MF_MSG_KERNEL_HIGH_ORDER: > p = pfn_to_online_page(pfn); > if (!p) > return true; > cpu_relax(); > return page_count(p) == 0 && > !PageLRU(p) && > !page_mapped(p) && > !page_folio(p)->mapping && > !is_free_buddy_page(p); > > > A buddy page being allocated must transit rmqueue() → prep_new_page() → > post_alloc_hook() before the caller can use it. Each step either bumps > _refcount or sets state we can observe (PageLRU, ->mapping). cpu_relax() > lets that remote-CPU progress become visible before we resample. > > A genuine non-buddy high-order kernel tail page stays unowned across the > recheck, so the panic still fires on the case this series targets. > > The window is much narrowed now, not eliminated — I'll say so in the changelog. > > I also added a selftest that enables the sysctl, injects MADV_HWPOISON > on a userspace anon page in a forked child, and asserts SIGBUS (not a > panic). I've been running this in a loop for hours, and I haven't seen any > false positive. The userspace anon pages are already allocated. Those pages are in a stable state. So your selftest cannot test above window. Or am I miss something? Thanks. .