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 BC2474963C8; Wed, 13 May 2026 15:40:21 +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=1778686823; cv=none; b=o75z0J1EaK/PPPL8J3U+keDfgpa48CMgHB1OIVelDGOac+XdBsfK/tl1q2KCGlS3PstcEg4ZNVVkOp6ncCzP5Pt2r4V3xIcsOZT9rKV6a5qxoWy8GZvi8q0JYWGByqeeXnLdfWBPO+pVADh1QxTm3iRQ6zH7L/tDp6VdC9y4pD4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778686823; c=relaxed/simple; bh=ncCft6wLVNRyu8CqP+C5ij+1shPAevwH/Ny4XjCyHOI=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=j477I3dV+OYZutQK6tCIZcSUygNNRMO+lqQm1xNf9p0SqWMVffn5tIfBe0sEypTYh1rPoyTjn6GYUrsUVbgLbmPiVGpn/s24k5iQ3AloHLqPprGW7//S4O/2xKPDbuLZIpU46q55vMWz07bYsPcs6+881sdXzs5HVn2PYD2uPzg= 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=MUz/a7yD; 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="MUz/a7yD" 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=ps5zJ4kvCPWwzd5UeBW/t615zOIlJIp4XGX6hA3qpRU=; b=MUz/a7yDPF3GUlgcn3qxI3gfXO vu0GqHwaV/Mb1bW82IvzWEIXuz1AjC5Kf2hZQhhXHM7cK/WFxIui/Cd+LceT7+B4TWxlF/y5O2o5V Ynyr/q5CC229E0JpqG/ofuV5CPL8tKnbhLV2UojmrnwyGZx02U7HgRK0SZ/4U98R3CXLsTObxtF4Q 8gPvehCcyeFI3RKI/DNCXG0nWLf2F803eE4PF4ug8dR562+Lae3fObfrgDoKgeS865C3f7su0x3tF DcDiLzTDw+HtJoxbAfkmpsusVnu8fI4Q/dYZoRN+va/uuESIhOwGl2i00Uv6IslMYqXmaHSgP6ynC jDONS5zA==; 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 1wNBh5-003GVI-14; Wed, 13 May 2026 15:40:19 +0000 From: Breno Leitao Date: Wed, 13 May 2026 08:39:37 -0700 Subject: [PATCH v7 6/6] Documentation: document panic_on_unrecoverable_memory_failure sysctl Precedence: bulk X-Mailing-List: linux-trace-kernel@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: <20260513-ecc_panic-v7-6-be2e578e61da@debian.org> References: <20260513-ecc_panic-v7-0-be2e578e61da@debian.org> In-Reply-To: <20260513-ecc_panic-v7-0-be2e578e61da@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=4856; i=leitao@debian.org; h=from:subject:message-id; bh=ncCft6wLVNRyu8CqP+C5ij+1shPAevwH/Ny4XjCyHOI=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBqBJs7zoPgDDOGBYZIRWE5RwFBx84GbKDJ1RbfP mV5jtA91a2JAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCagSbOwAKCRA1o5Of/Hh3 bZu2D/4gM6SMB3HsM1fzjJLPFg/Qj+o9TLUGhGX0U4PAr4DLJAFnRYhnbWfSnD6iqxo/aGpRGyp A4uC+3akefYTn2jttKvwNwQTz3K/dMC2u/ygdomRYAEJCzqah7oozi71XW7BJxV7GEzGuyggiDR nY1mzqHCNUC1/iWJB9Ptq5b+6tbCikpyCb5F9wQbk3B4tN9/g47cKcav0BJDax+dn15Pujh4laM y98k0W0fSNwDrJQySnNMOYZy0vraHPxo/gUc2EPLzOSEI8+RWGd3yuAmG4eK8PZrVG3Le/4e6to LzEAxARG4wZz1tvDYTNJegKeLJa8JYZPpHOgRE3WfYEreS76cQ2/4yujfr28kHniGRtDp+dU5O0 NHSJZTDB8MdO9wLjHpCmaanq0Sv+PCdxDX9llfKF57/gWSRPnRtJ/gmJaXNxdjjJjr77McAlIeI kW24yoCcw5pm7OTWQzM/Lh8UiJxWB8vI3ypt3TauIsmdojyATYMo7aUVL/GRSCQRFKxDZ2zy6Dz kRBbVBUj2QzfbkRmglwtI5hM4fxGA5JFyw+1+NGNI5e0MUJ+KIncw+XWiSiqMq1M2hNO+Vtxa2d l/gZCO7rSf4VOlydR7YnJkksXXBbj5lgIH68gjUg2h9McfRt8NUgNEHJT/Yn6cW4ncP+pC6u5DW pRlZ6VXaiL1vUrA== 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 | 80 +++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 97e12359775c9..452c2ab25b35e 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 +926,85 @@ 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 reserved (``PageReserved``) memory: firmware reservations, +the kernel image, vDSO, the zero page, and similar memblock-reserved +regions. These are owned by the kernel, are not managed by the page +allocator, and cannot be recovered by the memory failure handler. + +Other unrecoverable kernel-owned populations (slab, vmalloc, page +tables, kernel stacks, ...) are not currently covered by this +sysctl. The handler cannot reliably distinguish them from a +userspace folio temporarily off the LRU during migration or +compaction, and the cost of a false-positive panic on a recoverable +userspace page is too high. 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 in the future 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 ============================= -- 2.53.0-Meta