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bootmem/sparsemem: remove limit constraint in alloc_bootmem_section

commit f5bf18f upstream.

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 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
unconditionally remove the limit condition in alloc_bootmem_section,
meaning allocations are allowed to cross section boundaries (necessary
for systems of this size).

Johannes Weiner pointed out that if alloc_bootmem_section() no longer
guarantees section-locality, we need check_usemap_section_nr() to print
possible cross-dependencies between node descriptors and the usemaps
allocated through it.  That makes the two loops in
sparse_early_usemaps_alloc_node() identical, so re-factor the code a
bit.

[akpm@linux-foundation.org: code simplification]
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ben Herrenschmidt <benh@kernel.crashing.org>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  • Loading branch information...
commit 9565cb71a1c0fbeab977cc346063873319f1953d 1 parent 5c6156f
Nishanth Aravamudan authored gregkh committed
Showing with 13 additions and 22 deletions.
  1. +2 −3 mm/bootmem.c
  2. +11 −19 mm/sparse.c
View
5 mm/bootmem.c
@@ -768,14 +768,13 @@ void * __init alloc_bootmem_section(unsigned long size,
unsigned long section_nr)
{
bootmem_data_t *bdata;
- unsigned long pfn, goal, limit;
+ unsigned long pfn, goal;
pfn = section_nr_to_pfn(section_nr);
goal = pfn << PAGE_SHIFT;
- 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);
+ return alloc_bootmem_core(bdata, size, SMP_CACHE_BYTES, goal, 0);
}
#endif
View
30 mm/sparse.c
@@ -353,29 +353,21 @@ static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map,
usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nodeid),
usemap_count);
- if (usemap) {
- for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
- if (!present_section_nr(pnum))
- continue;
- usemap_map[pnum] = usemap;
- usemap += size;
+ if (!usemap) {
+ usemap = alloc_bootmem_node(NODE_DATA(nodeid), size * usemap_count);
+ if (!usemap) {
+ printk(KERN_WARNING "%s: allocation failed\n", __func__);
+ return;
}
- return;
}
- usemap = alloc_bootmem_node(NODE_DATA(nodeid), size * usemap_count);
- if (usemap) {
- for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
- if (!present_section_nr(pnum))
- continue;
- usemap_map[pnum] = usemap;
- usemap += size;
- check_usemap_section_nr(nodeid, usemap_map[pnum]);
- }
- return;
+ for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
+ if (!present_section_nr(pnum))
+ continue;
+ usemap_map[pnum] = usemap;
+ usemap += size;
+ check_usemap_section_nr(nodeid, usemap_map[pnum]);
}
-
- printk(KERN_WARNING "%s: allocation failed\n", __func__);
}
#ifndef CONFIG_SPARSEMEM_VMEMMAP
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