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 <[email protected]> --- Documentation/admin-guide/sysctl/vm.rst | 70 +++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 97e12359775c9..802c51ba8c43b 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 +926,75 @@ 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 kernel-owned pages that +the memory failure handler cannot recover: reserved pages +(``PageReserved``) and stable kernel pages that hwpoison cannot handle +(slab, vmalloc, page tables, kernel stacks, and similar non-LRU, +non-buddy pages). + +Other failure paths are intentionally left out because they can be +reached by transient races with the page allocator (an in-flight +buddy allocation has refcount 0 and is no longer on the buddy free +list, briefly), and panicking on them would risk killing the box for +a page that was actually destined for userspace where the standard +SIGBUS recovery path applies. Pages whose state could not be +classified at all are also not covered, 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
