[PATCH v6 3/4] mm/memory-failure: add panic option for unrecoverable pages

[Breno Leitao <leitao@debian.org>]

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 or a delayed crash at an
unrelated code path.

Panic eligibility is intentionally narrow: only MF_MSG_KERNEL with
result == MF_IGNORED panics. That covers reserved pages (PageReserved)
and the kernel page types that the prior patch promotes from
MF_MSG_GET_HWPOISON via MF_GET_PAGE_UNHANDLABLE — slab, vmalloc, page
tables, kernel stacks, and similar non-LRU/non-buddy kernel-owned pages.

All other action types are excluded:

- MF_MSG_GET_HWPOISON and MF_MSG_KERNEL_HIGH_ORDER can be reached by
  transient refcount 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 what
  is actually a recoverable userspace page.

- MF_MSG_UNKNOWN means identify_page_state() could not classify the
  page; that is precisely the wrong basis for a panic decision.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/memory-failure.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4210173060aac..e4a9ceacaf36b 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 +1292,18 @@ static void update_per_node_mf_stats(unsigned long pfn,
 	++mf_stats->total;
 }
 
+static bool panic_on_unrecoverable_mf(enum mf_action_page_type type,
+				      enum mf_result result)
+{
+	if (!sysctl_panic_on_unrecoverable_mf || result != MF_IGNORED)
+		return false;
+
+	if (type == MF_MSG_KERNEL)
+		return true;
+
+	return false;
+}
+
 /*
  * "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 +1321,9 @@ 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;
 }
 

-- 
2.53.0-Meta