[PATCH v8 1/6] mm/memory-failure: drop dead error_states[] entry for reserved pages

[Breno Leitao <leitao@debian.org>]

The first entry of error_states[],

	{ reserved,	reserved,	MF_MSG_KERNEL,	me_kernel },

is unreachable.  identify_page_state() has two callers, and neither
one can dispatch a PG_reserved page to me_kernel():

  * memory_failure() reaches identify_page_state() only after
    get_hwpoison_page() returned 1.  get_any_page() reaches that
    return only via __get_hwpoison_page(), which only takes a
    refcount when the page is HWPoisonHandlable().
    HWPoisonHandlable() is an allowlist for LRU, free-buddy, and
    (for soft-offline) movable_ops pages -- PG_reserved pages do
    not satisfy any of these, so they fail with -EBUSY/-EIO long
    before identify_page_state() runs.

  * try_memory_failure_hugetlb() reaches identify_page_state() only
    via the MF_HUGETLB_IN_USED branch, where the page is necessarily
    a hugetlb folio.  hugetlb folios don't carry PG_reserved at that
    point: hugetlb_folio_init_vmemmap() calls __folio_clear_reserved()
    during init, so the reserved entry would not match even if it
    were still present.

me_kernel() never executes and the entry exists only to be matched
against by code that cannot see it.

Drop the entry, the me_kernel() helper, and the now-unused
"reserved" macro.  Leave the MF_MSG_KERNEL enum value in place: it
remains part of the tracepoint and pr_err() string tables, and
follow-on work to classify unrecoverable kernel pages can reuse it
without churning the user-visible enum.

No functional change.

Suggested-by: David Hildenbrand <david@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/memory-failure.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 51508a55c405..f4d3e6e20e13 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -980,17 +980,6 @@ static bool has_extra_refcount(struct page_state *ps, struct page *p,
 	return false;
 }
 
-/*
- * Error hit kernel page.
- * Do nothing, try to be lucky and not touch this instead. For a few cases we
- * could be more sophisticated.
- */
-static int me_kernel(struct page_state *ps, struct page *p)
-{
-	unlock_page(p);
-	return MF_IGNORED;
-}
-
 /*
  * Page in unknown state. Do nothing.
  * This is a catch-all in case we fail to make sense of the page state.
@@ -1199,10 +1188,8 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 #define mlock		(1UL << PG_mlocked)
 #define lru		(1UL << PG_lru)
 #define head		(1UL << PG_head)
-#define reserved	(1UL << PG_reserved)
 
 static struct page_state error_states[] = {
-	{ reserved,	reserved,	MF_MSG_KERNEL,	me_kernel },
 	/*
 	 * free pages are specially detected outside this table:
 	 * PG_buddy pages only make a small fraction of all free pages.
@@ -1234,7 +1221,6 @@ static struct page_state error_states[] = {
 #undef mlock
 #undef lru
 #undef head
-#undef reserved
 
 static void update_per_node_mf_stats(unsigned long pfn,
 				     enum mf_result result)

-- 
2.54.0