While testing AMS (Active Memory Sharing) / CMO (Cooperative Memory
Overcommit) on powerpc, we tripped the following:
kernel BUG at mm/bootmem.c:483!
cpu 0x0: Vector: 700 (Program Check) at [c000000000c03940]
pc: c000000000a62bd8: .alloc_bootmem_core+0x90/0x39c
lr: c000000000a64bcc: .sparse_early_usemaps_alloc_node+0x84/0x29c
sp: c000000000c03bc0
msr: 8000000000021032
current = 0xc000000000b0cce0
paca = 0xc000000001d80000
pid = 0, comm = swapper
kernel BUG at mm/bootmem.c:483!
enter ? for help
[c000000000c03c80] c000000000a64bcc
.sparse_early_usemaps_alloc_node+0x84/0x29c
[c000000000c03d50] c000000000a64f10 .sparse_init+0x12c/0x28c
[c000000000c03e20] c000000000a474f4 .setup_arch+0x20c/0x294
[c000000000c03ee0] c000000000a4079c .start_kernel+0xb4/0x460
[c000000000c03f90] c000000000009670 .start_here_common+0x1c/0x2c
This is
BUG_ON(limit && goal + size > limit);
and after some debugging, it seems that
goal = 0x7ffff000000
limit = 0x80000000000
and sparse_early_usemaps_alloc_node ->
sparse_early_usemaps_alloc_pgdat_section -> alloc_bootmem_section calls
return alloc_bootmem_section(usemap_size() * count, section_nr);
This is on a system with 8TB available via the AMS pool, and as a quirk
of AMS in firmware, all of that memory shows up in node 0. So, we end up
with an allocation that will fail the goal/limit constraints. In theory,
we could "fall-back" to alloc_bootmem_node() in
sparse_early_usemaps_alloc_node(), but since we actually have HOTREMOVE
defined, we'll BUG_ON() instead. A simple solution appears to be to
disable the limit check if the size of the allocation in
alloc_bootmem_secition exceeds the section size.
Signed-off-by: Nishanth Aravamudan <nacc@xxxxxxxxxx>
Cc: Dave Hansen <haveblue@xxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Ben Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Robert Jennings <rcj@xxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
---
include/linux/mmzone.h | 2 ++
mm/bootmem.c | 5 ++++-
2 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 650ba2f..4176834 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -967,6 +967,8 @@ static inline unsigned long early_pfn_to_nid(unsigned long pfn)
* PA_SECTION_SHIFT physical address to/from section number
* PFN_SECTION_SHIFT pfn to/from section number
*/
+#define BYTES_PER_SECTION (1UL << SECTION_SIZE_BITS)
+
#define SECTIONS_SHIFT (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
#define PA_SECTION_SHIFT (SECTION_SIZE_BITS)
diff --git a/mm/bootmem.c b/mm/bootmem.c
index 668e94d..5cbbc76 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -770,7 +770,10 @@ void * __init alloc_bootmem_section(unsigned long size,
pfn = section_nr_to_pfn(section_nr);
goal = pfn << PAGE_SHIFT;
- limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;
+ if (size > BYTES_PER_SECTION)
+ limit = 0;
+ else
+ limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;
bdata = &bootmem_node_data[early_pfn_to_nid(pfn)];
return alloc_bootmem_core(bdata, size, SMP_CACHE_BYTES, goal, limit);
--
1.7.5.4
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