[PATCH 2/3] mm, meminit: Always return a valid node from early_pfn_to_nid

[Mel Gorman]

early_pfn_to_nid can return node 0 if a PFN is invalid on machines
that has no node 0. A machine with only node 1 was observed to crash
with the following message

 BUG: unable to handle kernel paging request at 000000000002a3c8
 PGD 0
 Modules linked in:
 Hardware name: Supermicro H8DSP-8/H8DSP-8, BIOS 080011  06/30/2006
 task: ffffffff81c0d500 ti: ffffffff81c00000 task.ti: ffffffff81c00000
 RIP: 0010:[<ffffffff816dbd63>]  [<ffffffff816dbd63>] reserve_bootmem_region+0x6a/0xef
 RSP: 0000:ffffffff81c03eb0  EFLAGS: 00010086
 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
 RDX: ffffffff81c03ec0 RSI: ffffffff81d205c0 RDI: ffffffff8213ee60
 R13: ffffea0000000000 R14: ffffea0000000020 R15: ffffea0000000020
 FS:  0000000000000000(0000) GS:ffff8800fba00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000000000002a3c8 CR3: 0000000001c06000 CR4: 00000000000006b0
 Stack:
  ffffffff81c03f00 0000000000000400 ffff8800fbfc3200 ffffffff81e2a2c0
  ffffffff81c03fb0 ffffffff81c03f20 ffffffff81dadf7d ffffea0002000040
  ffffea0000000000 0000000000000000 000000000000ffff 0000000000000001
 Call Trace:
  [<ffffffff81dadf7d>] free_all_bootmem+0x4b/0x12a
  [<ffffffff81d97122>] mem_init+0x70/0xa3
  [<ffffffff81d78f21>] start_kernel+0x25b/0x49b

The problem is that early_page_uninitialised uses the early_pfn_to_nid
helper which returns node 0 for invalid PFNs. No caller of early_pfn_to_nid
cares except early_page_uninitialised. This patch has early_pfn_to_nid
always return a valid node.

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.2+
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a19527aa4243..5a616de1adca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1097,7 +1097,7 @@ int __meminit early_pfn_to_nid(unsigned long pfn)
 	spin_lock(&early_pfn_lock);
 	nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
 	if (nid < 0)
-		nid = 0;
+		nid = first_online_node;
 	spin_unlock(&early_pfn_lock);
 
 	return nid;
-- 
2.6.4