Re: 2.6.28-rc9 panics with crashkernel=256M while booting

From: Andrew Morton
Date: Thu Dec 25 2008 - 02:36:34 EST


(cc's added)

On Wed, 24 Dec 2008 13:25:49 +0530 Chandru <chandru@xxxxxxxxxx> wrote:

> On a ppc machine booting linux-2.6.28-rc9 with crashkernel=256M@32M boot
> parameter causes the kernel to panic while booting. __Following are the console
> messages...

- Please put [patch] in the Subject: line of patches

- Please choose a suitable title, as per
Documentation/SubmittingPatches, section 15.

- Please cc suitable mailing lists and maintainers on bug reports and
on patches.



From: Chandru <chandru@xxxxxxxxxx>

When booted with crashkernel=224M@32M or any memory size less than this,
the system boots properly. The following was the observation.. The
system comes up with two nodes (0-256M and 256M-4GB). _The crashkernel
memory reservation spans across these two nodes. _The
mark_reserved_regions_for_nid() in arch/powerpc/mm/numa.c resizes the
reserved part of the memory within it as:

_ _ _ _ _ _ if (end_pfn > node_ar.end_pfn)
_ _ _ _ _ _ _ _ reserve_size = (node_ar.end_pfn << PAGE_SHIFT)
_ _ _ _ _ _ _ _ _ _ - (start_pfn << PAGE_SHIFT);


but the reserve_bootmem_node() in mm/bootmem.c raises the pfn value of end

_ _ end = PFN_UP(physaddr + size);

This causes end to get a value past the last page in the 0-256M node.
_Again when reserve_bootmem_node() returns,
_mark_reserved_regions_for_nid() loops around to set the rest of the
crashkernel memory in the next node as reserved. _ It references
NODE_DATA(node_ar.nid) and this causes another 'Oops: kernel access of bad
area' problem. The following changes made the system to boot with any
amount of crashkernel memory size.

Signed-off-by: Chandru S <chandru@xxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

arch/powerpc/mm/numa.c | 7 ++++---
mm/bootmem.c | 4 ++++
2 files changed, 8 insertions(+), 3 deletions(-)

diff -puN arch/powerpc/mm/numa.c~2628-rc9-panics-with-crashkernel=256m-while-booting arch/powerpc/mm/numa.c
--- a/arch/powerpc/mm/numa.c~2628-rc9-panics-with-crashkernel=256m-while-booting
+++ a/arch/powerpc/mm/numa.c
@@ -995,10 +995,11 @@ void __init do_init_bootmem(void)
start_pfn, end_pfn);

free_bootmem_with_active_regions(nid, end_pfn);
+ }
+
+ for_each_online_node(nid) {
/*
- * Be very careful about moving this around. Future
- * calls to careful_allocation() depend on this getting
- * done correctly.
+ * Be very careful about moving this around.
*/
mark_reserved_regions_for_nid(nid);
sparse_memory_present_with_active_regions(nid);
diff -puN mm/bootmem.c~2628-rc9-panics-with-crashkernel=256m-while-booting mm/bootmem.c
--- a/mm/bootmem.c~2628-rc9-panics-with-crashkernel=256m-while-booting
+++ a/mm/bootmem.c
@@ -375,10 +375,14 @@ int __init reserve_bootmem_node(pg_data_
unsigned long size, int flags)
{
unsigned long start, end;
+ bootmem_data_t *bdata = pgdat->bdata;

start = PFN_DOWN(physaddr);
end = PFN_UP(physaddr + size);

+ if (end > bdata->node_low_pfn)
+ end = bdata->node_low_pfn;
+
return mark_bootmem_node(pgdat->bdata, start, end, 1, flags);
}

_

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