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

From: Andrew Morton <[email-masked]>
Date: Wed, 24 Dec 2008 23:35:36 -0800

(cc's added)

On Wed, 24 Dec 2008 13:25:49 +0530 Chandru <[email-masked]> 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 <[email-masked]>

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 <[email-masked]>
Cc: Benjamin Herrenschmidt <[email-masked]>
Cc: Paul Mackerras <[email-masked]>
Signed-off-by: Andrew Morton <[email-masked]>
---

 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);
 }
 
_