Re: [PATCH v4 2/3] mm/memory-failure: add panic option for unrecoverable pages

Miaohe Lin
2026-04-22T03:36:15Z

On 2026/4/15 20:55, Breno Leitao wrote:
> Add a sysctl panic_on_unrecoverable_memory_failure that triggers a
> kernel panic when memory_failure() encounters pages that cannot be
> recovered. This provides a clean crash with useful debug information
> rather than allowing silent data corruption.
>
> The panic is triggered for three categories of unrecoverable failures,
> all requiring result == MF_IGNORED:
>
> - MF_MSG_KERNEL: reserved pages identified via PageReserved.
>
> - MF_MSG_KERNEL_HIGH_ORDER: pages with refcount 0 that are not in the
> buddy allocator (e.g., tail pages of high-order kernel allocations).
> A TOCTOU race between get_hwpoison_page() and is_free_buddy_page()
> is possible when CONFIG_DEBUG_VM is disabled, since check_new_pages()
> is gated by is_check_pages_enabled() and becomes a no-op. Panicking
> is still correct: the physical memory has a hardware error regardless
> of who allocated the page.

What if the page is used by userspace? We can recover from later accessing.
Would panic here be overkill?

Thanks.
.

>
> - MF_MSG_UNKNOWN: pages that do not match any known recoverable state
> in error_states[]. A theoretical false positive from concurrent LRU
> isolation is mitigated by identify_page_state()'s two-pass design
> which rechecks using saved page_flags.
>
> MF_MSG_GET_HWPOISON is intentionally excluded: it covers both
> non-reserved kernel memory (SLAB/SLUB, vmalloc, kernel stacks, page
> tables) and transient refcount races, so panicking would risk false
> positives.
>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
> mm/memory-failure.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 81 insertions(+)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7b67e43dafbd1..311344f332449 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -74,6 +74,8 @@ static int sysctl_memory_failure_recovery __read_mostly = 1;
>
> static int sysctl_enable_soft_offline __read_mostly = 1;
>
> +static int sysctl_panic_on_unrecoverable_mf __read_mostly;
> +
> atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
>
> static bool hw_memory_failure __read_mostly = false;
> @@ -155,6 +157,15 @@ static const struct ctl_table memory_failure_table[] = {
> .proc_handler = proc_dointvec_minmax,
> .extra1 = SYSCTL_ZERO,
> .extra2 = SYSCTL_ONE,
> + },
> + {
> + .procname = "panic_on_unrecoverable_memory_failure",
> + .data = &sysctl_panic_on_unrecoverable_mf,
> + .maxlen = sizeof(sysctl_panic_on_unrecoverable_mf),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = SYSCTL_ONE,
> }
> };
>
> @@ -1281,6 +1292,59 @@ static void update_per_node_mf_stats(unsigned long pfn,
> ++mf_stats->total;
> }
>
> +/*
> + * Determine whether to panic on an unrecoverable memory failure.
> + *
> + * Design rationale: This design opts for immediate panic on kernel memory
> + * failures, capturing clean crashes rather than random crashes on MF_IGNORED
> + * pages.
> + *
> + * This panics on three categories of failures (all requiring result ==
> + * MF_IGNORED, meaning the page was not recovered):
> + *
> + * - MF_MSG_KERNEL: Reserved pages (identified via PageReserved) that belong
> + * to the kernel and cannot be recovered.
> + *
> + * - MF_MSG_KERNEL_HIGH_ORDER: Pages that get_hwpoison_page() observed as free
> + * (refcount 0) but are not in the buddy allocator. These are kernel pages
> + * in a transient state between allocation and freeing. A TOCTOU race
> + * (page allocated between get_hwpoison_page() and is_free_buddy_page())
> + * is possible when CONFIG_DEBUG_VM is disabled, since check_new_pages()
> + * is gated by is_check_pages_enabled() and becomes a no-op. However,
> + * panicking is still correct in this case: the physical memory has a
> + * hardware error, so an allocated hwpoisoned page is unrecoverable.
> + *
> + * - MF_MSG_UNKNOWN: Pages that reached identify_page_state() but did not
> + * match any known recoverable state in error_states[]. This is the
> + * catch-all for pages whose flags do not indicate a recoverable user or
> + * cache page (no LRU, no swapcache, no mlock, etc). A theoretical false
> + * positive exists if concurrent LRU isolation clears PG_lru between
> + * folio_lock() and saving page_flags, but this window is very narrow and
> + * mitigated by identify_page_state()'s two-pass design which rechecks
> + * using saved page_flags.
> + *
> + * Pages intentionally NOT included:
> + * - MF_MSG_GET_HWPOISON: get_hwpoison_page() failure on non-reserved pages.
> + * This includes dynamically allocated kernel memory (SLAB/SLUB, vmalloc,
> + * kernel stacks, page tables) which are not PageReserved and fail
> + * get_hwpoison_page() with -EBUSY/-EIO. These share the return path with
> + * transient refcount races, so panicking here would risk false positives.
> + *
> + * Note: Some transient races in the buddy allocator path are mitigated by
> + * memory_failure()'s retry mechanism. When take_page_off_buddy() fails,
> + * the code clears PageHWPoison and retries the entire memory_failure()
> + * flow, allowing pages to be properly reclassified with updated flags.
> + */
> +static bool panic_on_unrecoverable_mf(enum mf_action_page_type type,
> + enum mf_result result)
> +{
> + return sysctl_panic_on_unrecoverable_mf &&
> + result == MF_IGNORED &&
> + (type == MF_MSG_KERNEL ||
> + type == MF_MSG_KERNEL_HIGH_ORDER ||
> + type == MF_MSG_UNKNOWN);
> +}
> +
> /*
> * "Dirty/Clean" indication is not 100% accurate due to the possibility of
> * setting PG_dirty outside page lock. See also comment above set_page_dirty().
> @@ -1298,6 +1362,9 @@ static int action_result(unsigned long pfn, enum mf_action_page_type type,
> pr_err("%#lx: recovery action for %s: %s\n",
> pfn, action_page_types[type], action_name[result]);
>
> + if (panic_on_unrecoverable_mf(type, result))
> + panic("Memory failure: %#lx: unrecoverable page", pfn);
> +
> return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
> }
>
> @@ -2428,6 +2495,20 @@ int memory_failure(unsigned long pfn, int flags)
> }
> res = action_result(pfn, MF_MSG_BUDDY, res);
> } else {
> + /*
> + * The page has refcount 0 but is not in the buddy
> + * allocator — it is a non-compound high-order kernel
> + * page (e.g., a tail page of a high-order allocation).
> + *
> + * A TOCTOU race where the page transitions from
> + * free-buddy to allocated between get_hwpoison_page()
> + * and is_free_buddy_page() is possible when
> + * CONFIG_DEBUG_VM is disabled (check_new_pages() is
> + * gated by is_check_pages_enabled() and becomes a
> + * no-op). Panicking is still correct: the physical
> + * memory has a hardware error regardless of who
> + * allocated the page.
> + */
> res = action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
> }
> goto unlock_mutex;
>