linux-kernel - [PATCH] mm/page_alloc: fix boot hang in memmap_init

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Date:   Tue, 13 Mar 2018 23:42:40 +0100
From:   Daniel Vacek <neelx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Daniel Vacek <neelx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Paul Burton <paul.burton@...tec.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, stable@...r.kernel.org
Subject: [PATCH] mm/page_alloc: fix boot hang in memmap_init_zone

On some architectures (reported on arm64) commit 864b75f9d6b01 ("mm/page_alloc: fix memmap_init_zone pageblock alignment")
causes a boot hang. This patch fixes the hang making sure the alignment
never steps back.

Link: http://lkml.kernel.org/r/0485727b2e82da7efbce5f6ba42524b429d0391a.1520011945.git.neelx@redhat.com
Fixes: 864b75f9d6b01 ("mm/page_alloc: fix memmap_init_zone pageblock alignment")
Signed-off-by: Daniel Vacek <neelx@...hat.com>
Tested-by: Sudeep Holla <sudeep.holla@....com>
Tested-by: Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Paul Burton <paul.burton@...tec.com>
Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: <stable@...r.kernel.org>
---
 mm/page_alloc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3d974cb2a1a1..e033a6895c6f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5364,9 +5364,14 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 			 * is not. move_freepages_block() can shift ahead of
 			 * the valid region but still depends on correct page
 			 * metadata.
+			 * Also make sure we never step back.
 			 */
-			pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
+			unsigned long next_pfn;
+
+			next_pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
 					~(pageblock_nr_pages-1)) - 1;
+			if (next_pfn > pfn)
+				pfn = next_pfn;
 #endif
 			continue;
 		}
-- 
2.16.2