When the memory failure handler encounters an in-use kernel page that it
cannot recover (slab, page tables, kernel stacks, vmalloc, etc.), it
currently logs the error as "Ignored" and continues operation.

This leaves corrupted data accessible to the kernel, which will inevitably
cause either silent data corruption or a delayed crash when the poisoned memory
is next accessed.

This is a common problem on large fleets. We frequently observe multi-bit ECC
errors hitting kernel slab pages, where memory_failure() fails to recover them
and the system crashes later at an unrelated code path, making root cause
analysis unnecessarily difficult.

Here is one specific example from production on an arm64 server: a multi-bit
ECC error hit a dentry cache slab page, memory_failure() failed to recover it
(slab pages are not supported by the hwpoison recovery mechanism), and 67
seconds later d_lookup() accessed the poisoned cache line causing a synchronous
external abort:

    [88690.479680] [Hardware Error]: error_type: 3, multi-bit ECC
    [88690.498473] Memory failure: 0x40272d: unhandlable page.
    [88690.498619] Memory failure: 0x40272d: recovery action for
                   get hwpoison page: Ignored
    ...
    [88757.847126] Internal error: synchronous external abort:
                   0000000096000410 [#1] SMP
    [88758.061075] pc : d_lookup+0x5c/0x220

This series adds a new sysctl vm.panic_on_unrecoverable_memory_failure
(default 0) that, when enabled, panics immediately on unrecoverable
memory failures. This provides a clean crash dump at the time of the
error, which is far more useful for diagnosis than a random crash later
at an unrelated code path.

This also categorizes reserved pages as MF_MSG_KERNEL, and panics on
unknown page types (MF_MSG_UNKNOWN), so all unrecoverable failure cases
are covered.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v2:
- Panic on MF_MSG_KERNEL, MF_MSG_KERNEL_HIGH_ORDER and MF_MSG_UNKNOWN
  instead of MF_MSG_GET_HWPOISON.
- Report MF_MSG_KERNEL for reserved pages when get_hwpoison_page() fails
  instead of MF_MSG_GET_HWPOISON.
- Link to v1: https://patch.msgid.link/20260323-ecc_panic-v1-0-72a1921726c5@debian.org

---
Breno Leitao (3):
      mm/memory-failure: report MF_MSG_KERNEL for reserved pages
      mm/memory-failure: add panic_on_unrecoverable_memory_failure sysctl
      Documentation: document panic_on_unrecoverable_memory_failure sysctl

 Documentation/admin-guide/sysctl/vm.rst | 27 +++++++++++++++++++++++++++
 mm/memory-failure.c                     | 22 +++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)
---
base-commit: c369299895a591d96745d6492d4888259b004a9e
change-id: 20260323-ecc_panic-4e473b83087c

Best regards,
--  
Breno Leitao <leitao@debian.org>