From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD2DA31F9A6; Wed, 27 May 2026 14:06:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779890817; cv=none; b=ppZYQ+5yKFPJiw7zOG4rid36Zqs2t7RT3w58xTw1d9N+rh+1wp5vK6MsSNiqrp8KEcTYIlLKIw402KQBGBQGbFauDz9Dotct4B/1Rc7ZGyBTj3y7XL7QFkdiPhn9alBhLWroBIHqN3vZL3qcaXsEZpIjEleDJoTVlmTvbW4RZqs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779890817; c=relaxed/simple; bh=B5KdTD7ZhP/7hHR5QHSstU2DTYx/6InnYGWHrgT3KG0=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=lPtdwskGiMJ39RwL5reBqEhQXIvx/+kLOjNL1A7zpJBHkGzSUd7OBoMdnjZlX85q9bZouSvJtAbe5+PWEABW+CxV7fkwnaDLV2uVajdPCqm0MMUx+CmEGiY3ZsEMDLTo9bLBT4OU/eLWs4SbRx6a4o0rhJJANZZtjVGPcp9EbUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=JHUaBSOJ; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="JHUaBSOJ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:Cc:To:In-Reply-To:References: Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description; bh=qvNiDGBgEtWh04CKORYdnjbOWGHx4PFQRMc8UbqA0bc=; b=JHUaBSOJnq5vadUYwzmkHoaMjm 1k53DUwYyVs12ddAPrAOBff7ga+He6A7EGRfQO2BZQn84C6hR3PyatneMWAHX6WBsy2rxzLMhhoT6 p2+/dn7sshOf9yKbfvNjzmESoK/FaQ9FXOJDZ+GLMu4+4VFrVhfTJkMQNv1hB5lb+VqiFREGTkNLu pBYRwsfbX5Wt7d8lMVF3Ua0Obts18Yv8jOXl26BPM+sd5pfLJR+t+DbDtLO9Zq4xMw+m/U/8vM7sx bOkKl5OFqZU5bulJTJIeW/JerxVH6cE5xtV3kKxfYPr2laAhbHkId6x8pZ2PLp0A6SoLv8B2DgwEf ATUcNy2g==; 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 1wSEuM-003DTr-0H; Wed, 27 May 2026 14:06:54 +0000 From: Breno Leitao Date: Wed, 27 May 2026 07:06:18 -0700 Subject: [PATCH v8 5/6] Documentation: document panic_on_unrecoverable_memory_failure sysctl Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20260527-ecc_panic-v8-5-9ea0cfa16bb0@debian.org> References: <20260527-ecc_panic-v8-0-9ea0cfa16bb0@debian.org> In-Reply-To: <20260527-ecc_panic-v8-0-9ea0cfa16bb0@debian.org> To: Miaohe Lin , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Naoya Horiguchi , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , "Liam R. Howlett" , "Liam R. Howlett" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Breno Leitao , linux-trace-kernel@vger.kernel.org, kernel-team@meta.com X-Mailer: b4 0.16-dev-d5d98 X-Developer-Signature: v=1; a=openpgp-sha256; l=5051; i=leitao@debian.org; h=from:subject:message-id; bh=B5KdTD7ZhP/7hHR5QHSstU2DTYx/6InnYGWHrgT3KG0=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBqFvpbWFZ5tW+B7rNgwndjLhTSZaqZDyApt28GJ Z+2hgOzjLKJAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCahb6WwAKCRA1o5Of/Hh3 bcF1D/96nl3pHZvVsIHDOBSzXfwQzAgISt292m7aKGeL5wOoHLfNVNRDP/Qay3Zw8ihSmZ3SKhq eCtGDDDFkRK8DyONcMBfMNzcU10qbErfG4WjyHM6o8G0vrPAwDC0PD/7lHc2+JmsEadaFvww+XM /a8NP520hvDMj5SFWLtm6SLqzLvIoDLfy5Xuq29WYmniC/kGgBFhZ/AOHulYeBwUD/9rzcvmIwj RFNtYgjZ9sFtDVZ4qCM3BWaxuNtoZId2vtOhOK4Uz4q4+D+5kBItasimM6zOdGS5mea++lWcj0f baLqPbPYDyM1mV/Ll8+3kqjZSZmh9DyW//0FUVQAGKFkH6lqVXx+C3t88ItZWnc/ULK+PvMqAa8 qnRQxkc4RXfAjoDeIZrqro8Qk/HgJWt37VUlbMM2rziXTB70YS7yZNWFf1gn5um8U2YPuOqeMVH O+UxsbKgQA7K0qX4ZQH9HwI2+MG25WFZMXd0PUj7dEkmnKfTo79y4dsVIgDzuaLD3KLCz2hETY9 Gdj6pWYpUvRsPFL8trBz7mnqNo3wY05zjlGAGglp3LZG+rJ5igsTHRWRuc6IpfmMSA/RXwxIC74 k9cAj6ATDQ8kYFXomnrW7iWMIrt5eKqdCs1apuDfCNcqV25ZjgZ6cT5XDp0P/28x8DWsecAWbUn GG9y0sD0/WbbUEA== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D X-Debian-User: leitao Add documentation for the new vm.panic_on_unrecoverable_memory_failure sysctl, describing which failures trigger a panic (kernel-owned pages the handler cannot recover) and which are intentionally left out (transient allocator races and unclassified pages). Signed-off-by: Breno Leitao --- Documentation/admin-guide/sysctl/vm.rst | 85 +++++++++++++++++++++++++++++++++ 1 file changed, 85 insertions(+) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 97e12359775c..f71d87039904 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -67,6 +67,7 @@ Currently, these files are in /proc/sys/vm: - page-cluster - page_lock_unfairness - panic_on_oom +- panic_on_unrecoverable_memory_failure - percpu_pagelist_high_fraction - stat_interval - stat_refresh @@ -925,6 +926,90 @@ panic_on_oom=2+kdump gives you very strong tool to investigate why oom happens. You can get snapshot. +panic_on_unrecoverable_memory_failure +====================================== + +When a hardware memory error (e.g. multi-bit ECC) hits a kernel page +that cannot be recovered by the memory failure handler, the default +behaviour is to ignore the error and continue operation. This is +dangerous because the corrupted data remains accessible to the kernel, +risking silent data corruption or a delayed crash when the poisoned +memory is next accessed. + +When enabled, this sysctl triggers a panic on memory failure events +hitting kernel-owned pages that the handler cannot recover: +``PageReserved`` (firmware reservations, kernel image, vDSO, zero +page, and similar memblock-reserved regions), ``PageSlab``, +``PageTable``, and ``PageLargeKmalloc``. These are owned by the +kernel and the memory failure handler cannot reliably evict their +contents. + +For soft offline (``madvise(MADV_SOFT_OFFLINE)``, +``/sys/devices/system/memory/soft_offline_page``), pages owned by +``movable_ops`` are exempted, since soft offline is allowed to +migrate them even though they are not on the LRU. + +Other unrecoverable kernel-owned populations (vmalloc allocations, +kernel stack pages, ...) are not currently covered because the +handler has no page-type signal that distinguishes them from a +userspace folio temporarily off the LRU during migration or +compaction. Such pages still go through the standard +MF_MSG_GET_HWPOISON path: ``PG_hwpoison`` is set on them and a +delayed crash on the next access remains possible. Coverage may +grow as the handler gains stronger kernel-ownership signals. + +Recoverable failure paths are also intentionally left out: in-flight +buddy allocations and other transient races with the page allocator +can reach the same diagnostic, and panicking on them would risk +killing the box for a page destined for userspace where the standard +SIGBUS recovery path applies. Pages whose state could not be +classified at all are not covered either, since an unknown state is +not a sound basis for a panic decision. + +For many environments it is preferable to panic immediately with a clean +crash dump that captures the original error context, rather than to +continue and face a random crash later whose cause is difficult to +diagnose. + +Use cases +--------- + +This option is most useful in environments where unattributed crashes +are expensive to debug or where data integrity must take precedence +over availability: + +* Large fleets, where multi-bit ECC errors on kernel pages are observed + regularly and post-mortem analysis of an unrelated downstream crash + (often seconds to minutes after the original error) consumes + significant engineering effort. + +* Systems configured with kdump, where panicking at the moment of the + hardware error produces a vmcore that still contains the faulting + address, the affected page state, and the originating MCE/GHES + record — context that is typically lost by the time a delayed crash + occurs. + +* High-availability clusters that rely on fast, deterministic node + failure for failover, and prefer an immediate panic over silent data + corruption propagating to replicas or persistent storage. + +* Kernel and platform developers reproducing hwpoison issues with + tools such as ``mce-inject`` or error-injection debugfs interfaces, + where panicking on the unrecoverable path makes regressions + immediately visible instead of surfacing as later, unrelated + failures. + += ===================================================================== +0 Try to continue operation (default). +1 Panic immediately. If the ``panic`` sysctl is also non-zero then the + machine will be rebooted. += ===================================================================== + +Example:: + + echo 1 > /proc/sys/vm/panic_on_unrecoverable_memory_failure + + percpu_pagelist_high_fraction ============================= -- 2.54.0