[RFC PATCH] driver: base: memory: Maintain correct mem->end_section_nr when memory block is partially filled

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

Last section of memory block is always initialized to

mem->start_section_nr + sections_per_block - 1

which will not be true for a section that doesn't contain sections_per_block
sections due to the memory size specified. This causes the following
kernel crash when memory blocks under a node are registered during reboot
that follows a memory hotplug operation on pseries guest.

Unable to handle kernel paging request for data at address 0xf0000000003f0020
Faulting instruction address: 0xc0000000007657cc
Oops: Kernel access of bad area, sig: 11 [#1]
SMP NR_CPUS=1024 NUMA pSeries

Modules linked in:

CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6+ #48
task: c0000000ba3c0000 ti: c00000013c580000 task.ti: c00000013c580000
NIP: c0000000007657cc LR: c000000000592dbc CTR: 0000000000000400
REGS: c00000013c5836f0 TRAP: 0300   Not tainted  (4.2.0-rc6+)
MSR: 8000000000009032  MSR: 8000000000009032 <<SFSF,EE,EE,ME,ME,IR,IR,DR,DR,RI,RI>>  CR: 48000048  XER: 00000000
  CR: 48000048  XER: 00000000
CFAR: 00003fff990f50ec CFAR: 00003fff990f50ec DAR: f0000000003f0020 DSISR: 40000000 DAR: f0000000003f0020 DSISR: 40000000 SOFTE: 1 SOFTE: 1
GPR00: c000000000592dbc c000000000592dbc c00000013c583970 c00000013c583970 c0000000014f0300 c0000000014f0300 00000000003f0000 00000000003f0000
GPR04: 0000000000000000 0000000000000000 c0000000f43b2900 c0000000f43b2900 c0000000ba324668 c0000000ba324668 0000000000000001 0000000000000001
GPR08: c000000001540300 c000000001540300 f000000000000000 f000000000000000 f0000000003f0000 f0000000003f0000 0000000000000001 0000000000000001
GPR12: 0000000024000084 0000000024000084 c00000000ff20000 c00000000ff20000 c00000000000b5b0 c00000000000b5b0 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR24: c00000000188c380 c00000000188c380 0000000000000000 0000000000000000 0000000000014000 0000000000014000 c0000000018b54e8 c0000000018b54e8
GPR28: c00000013c06e800 c00000013c06e800 000000000000ffff 000000000000ffff 0000000000000000 0000000000000000 000000000000fc00 000000000000fc00

NIP [c0000000007657cc] .get_nid_for_pfn+0x2c/0x60
LR [c000000000592dbc] .register_mem_sect_under_node+0x8c/0x150
Call Trace:
[c00000013c583970] [c00000000056e44c] .put_device+0x2c/0x50
[c00000013c5839f0] [c000000000592dbc] .register_mem_sect_under_node+0x8c/0x150
[c00000013c583a80] [c0000000005932b4] .register_one_node+0x2c4/0x380
[c00000013c583b30] [c000000000c882b8] .topology_init+0x44/0x1e0
[c00000013c583bf0] [c00000000000ad30] .do_one_initcall+0x110/0x270
[c00000013c583ce0] [c000000000c845d4] .kernel_init_freeable+0x278/0x360
[c00000013c583db0] [c00000000000b5d4] .kernel_init+0x24/0x130
[c00000013c583e30] [c0000000000094e8] .ret_from_kernel_thread+0x58/0x70

Fix this by updating the memory block to always contain the right
number of sections instead of assuming sections_per_block.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
---
 drivers/base/memory.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 2804aed..7f3ce2e 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -645,6 +645,7 @@ static int add_memory_block(int base_section_nr)
 	if (ret)
 		return ret;
 	mem->section_count = section_count;
+        mem->end_section_nr = mem->start_section_nr + section_count -1;
 	return 0;
 }
 
-- 
2.1.0