[PATCH] fixup for "mm: refactor initialization of stuct page for holes"

[Mike Rapoport]

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---
 mm/page_alloc.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ce2bdaabdf96..86fde4424e87 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6227,7 +6227,8 @@ void __init __weak memmap_init(unsigned long size, int nid,
 			       unsigned long zone,
 			       unsigned long range_start_pfn)
 {
-	unsigned long start_pfn, end_pfn, next_pfn = 0;
+	static unsigned long hole_start_pfn;
+	unsigned long start_pfn, end_pfn;
 	unsigned long range_end_pfn = range_start_pfn + size;
 	u64 pgcnt = 0;
 	int i;
@@ -6235,7 +6236,6 @@ void __init __weak memmap_init(unsigned long size, int nid,
 	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
 		start_pfn = clamp(start_pfn, range_start_pfn, range_end_pfn);
 		end_pfn = clamp(end_pfn, range_start_pfn, range_end_pfn);
-		next_pfn = clamp(next_pfn, range_start_pfn, range_end_pfn);
 
 		if (end_pfn > start_pfn) {
 			size = end_pfn - start_pfn;
@@ -6243,10 +6243,10 @@ void __init __weak memmap_init(unsigned long size, int nid,
 					 MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
 		}
 
-		if (next_pfn < start_pfn)
-			pgcnt += init_unavailable_range(next_pfn, start_pfn,
-							zone, nid);
-		next_pfn = end_pfn;
+		if (hole_start_pfn < start_pfn)
+			pgcnt += init_unavailable_range(hole_start_pfn,
+							start_pfn, zone, nid);
+		hole_start_pfn = end_pfn;
 	}
 
 	/*
@@ -6256,8 +6256,8 @@ void __init __weak memmap_init(unsigned long size, int nid,
 	 * considered initialized. Make sure that memmap has a well defined
 	 * state.
 	 */
-	if (next_pfn < range_end_pfn)
-		pgcnt += init_unavailable_range(next_pfn, range_end_pfn,
+	if (hole_start_pfn < range_end_pfn)
+		pgcnt += init_unavailable_range(hole_start_pfn, range_end_pfn,
 						zone, nid);
 
 	if (pgcnt)
-- 
2.28.0

...

> From 89469f063c192ae70aea0bd6e1e2a7e99894e5b6 Mon Sep 17 00:00:00 2001
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Date: Wed, 2 Dec 2020 23:23:26 -0500
> Subject: [PATCH 1/1] mm: initialize struct pages in reserved regions outside
>  of the zone ranges
> 
> pfn 0 wasn't initialized and the PagePoison remained set when
> reserve_bootmem_region() called __SetPageReserved, inducing a silent
> boot failure with DEBUG_VM (and correctly so, because the crash
> signaled the nodeid/nid of pfn 0 would be again wrong).
> 
> Without this change, the pfn 0 part of a memblock.reserved range,
> isn't in any zone spanned range, nor in any nid spanned range, when we
> initialize the memblock.memory holes pfn 0 won't be included because
> it has no nid and no zoneid.
> 
> There's no enforcement that all memblock.reserved ranges must overlap
> memblock.memory ranges, so the memblock.reserved ranges also require
> an explicit initialization and the zones and nid ranges need to be
> extended to include all memblock.reserved ranges with struct pages, or
> they'll be left uninitialized with PagePoison as it happened to pfn 0.
 
I rather think that we should enforce the overlap between
memblock.reserved and memblock.memory. If there are regions that cannot
be mapped, we have other ways to deal with that (e.g. MEMBLOCK_NOMAP)
instead of dropping these ranges from memblock.memory.

> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> ---
>  include/linux/memblock.h | 17 +++++++++---
>  mm/debug.c               |  3 ++-
>  mm/memblock.c            |  4 +--
>  mm/page_alloc.c          | 57 ++++++++++++++++++++++++++++++++--------
>  4 files changed, 63 insertions(+), 18 deletions(-)
> 

-- 
Sincerely yours,
Mike.