From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0F88AFE5214 for ; Fri, 24 Apr 2026 12:01:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7BC1D6B008C; Fri, 24 Apr 2026 08:01:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 76D6C6B0093; Fri, 24 Apr 2026 08:01:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 65C226B0096; Fri, 24 Apr 2026 08:01:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 4F39C6B008C for ; Fri, 24 Apr 2026 08:01:22 -0400 (EDT) Received: from smtpin05.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay05.hostedemail.com (Postfix) with ESMTP id F02E54014A for ; Fri, 24 Apr 2026 12:01:21 +0000 (UTC) X-FDA: 84693309162.05.E95B499 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) by imf24.hostedemail.com (Postfix) with ESMTP id 1F4A518000D for ; Fri, 24 Apr 2026 12:01:19 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=XXhpjgvn; spf=none (imf24.hostedemail.com: domain of leitao@debian.org has no SPF policy when checking 82.195.75.108) smtp.mailfrom=leitao@debian.org; dmarc=pass (policy=none) header.from=debian.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777032080; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=i9gfDuuaXGFcGzcTQeLr1pg8fqm0C7Flns4/9cvFi4g=; b=pJTrQ3m70XaP+/3oNve2jEPz5+XeS73SyX+F5iwSoLsWvQUmhGN5bHwQV7V3Y5CMib1My4 lOv+C62CrBkAOOKJLo5uY38g1s2abpbT8CubM9YMwwwKPI8tJy5fkhFprcS9iAVYx8Euet OMZfhbbkBAWCwKq9xH4T+MwayP/0E/E= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777032080; a=rsa-sha256; cv=none; b=SK2CdmHi6aCBllkNg/OqT4pPLx0wvoJWkl/VLqXlhSrwJBZFF+rWxuUEwj6LhH8XsPWYTd H1QH9HYCNJAUu1OITIWT1mJ+eGWlYUljUq7ziZj9dLchglD7b2cCBhCOlmpqU/d9pV2bOm BYLJtmL3QM0hG9/wMDNnJxx2Atu0KxI= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=XXhpjgvn; spf=none (imf24.hostedemail.com: domain of leitao@debian.org has no SPF policy when checking 82.195.75.108) smtp.mailfrom=leitao@debian.org; dmarc=pass (policy=none) header.from=debian.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Reply-To:Content-ID:Content-Description; bh=i9gfDuuaXGFcGzcTQeLr1pg8fqm0C7Flns4/9cvFi4g=; b=XXhpjgvn+c0oE9J0xyNK5mpMTS kUx+kT9SiAQJQHow1kuklllfRYjp1nacBmIV6NiAm/4iuo9zbo2lQ1vk2QMuF/Esq985vSWJtpHH6 onBsQragEGxgW8PFJ9SQZ/kB3P+ktm0N+nqjXTxia0n6bW449lIyALBK8wobcvq9eS+rGZChiCBPU O+/ml6KOuQugS7YhUCdPf8qPgzTIuUaexfm26y8itblIlcOGXAnxNRq07GFDLeBrqcCQKKlIGhGQr HyQc51x84G0ritTwD28VsX+RGp5ar9kMoruGbjgnfZewEtZl9FqpY+b+mznM4BVfzx5CmAz6IXf5Z d8WmURlQ==; Received: from authenticated user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wGFDW-0039ct-3A; Fri, 24 Apr 2026 12:01:07 +0000 Date: Fri, 24 Apr 2026 05:01:01 -0700 From: Breno Leitao To: Miaohe Lin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com, Naoya Horiguchi , Andrew Morton , Jonathan Corbet , Shuah Khan , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Subject: Re: [PATCH v4 2/3] mm/memory-failure: add panic option for unrecoverable pages Message-ID: References: <20260415-ecc_panic-v4-0-2d0277f8f601@debian.org> <20260415-ecc_panic-v4-2-2d0277f8f601@debian.org> <6b505601-747a-0812-7544-63a8ab3cffce@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Debian-User: leitao X-Stat-Signature: 7w9rq9dqjiy793a34sezy8dd6gooonxt X-Rspam-User: X-Rspamd-Queue-Id: 1F4A518000D X-Rspamd-Server: rspam05 X-HE-Tag: 1777032079-219636 X-HE-Meta: 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 lvoUZGVS yF2XJlHeSddoRED3b4MFpTXSzFq5J6PM1KzJ8AcMJ9mjvXsvk2LD/2Db2iu0wy+CdAHE01X+LvoYrYWZfFOBpAEEG2Yi/G2JGOWiEhNDHc3VZ4YG3m36eXcflRQ/dziLVFtnIfoxbdwcJNo4QoxWS2EzTh+mypz7gAH2w9Moz4etpwaLso1tiogHnEfU/2j1A5yliQh8rhNEso3ogQShRZQju7LXL2luK8fQVZ4hUOhAAlJjTlMnyvo/0v95oSSqbht18EbXiBBLG89Z1O4qfu2v6XzeFvAbkGx3StDpuYI9J0PE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Thanks for the review, --breno