linux-kernel - [PATCH] Fix spurious BUG_ON() in mark

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Date:	Wed, 09 Jul 2008 17:09:32 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...urebad.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] Fix spurious BUG_ON() in mark_bootmem()

Against:  2.6.26-rc8-mm1

Fixes problem introduced by patches:

bootmem-factor-out-the-marking-of-a-pfn-range.patch
bootmem-replace-node_boot_start-in-struct-bootmem_data.patch

HP ia64 NUMA platform fails to boot 26-rc8-mm1, hitting BUG_ON()
in mm/bootmem.c:mark_bootmem().

After linking all bootmem chunks, the 'bdata_list' on HP ia64 numa
platforms looks something like this:

        node 4:  0x0-0x8000
        node 0:  0x1c008000-0x1c07ec00
        node 1:  0x1c800000-0x1c87f000
        node 2:  0x1d000000-0x1d07f000
        node 3:  0x1d800000-0x1d87f000

[Node 4 is a pseudo-node generated by the platform firmware to
contain a configurable amount of zero-based, hardware interleaved
memory. 0x8000 pages or 512M is the minimum that can be configured.]

First call to mark_bootmem() [from free_bootmem()] called with:

	start-end:  0x1c008063-0x1c008262, reserve: 0, flags: 0

I.e, NOT in the first chunk of the list.

However, the "if (pos < bdata->node_min_pfn)" in the loop fails
to test the start address of the argument range [in 'pos'] against
the end of the chunk.  So, it treats the range as being in the node
4 chunk.  Second time thru' the loop, pos == 0x8000 is <
bdata->node_min_pfn and pos != start, so we trip the BUG_ON().

This patch enhances the if condition to skip chunks that do not
overlap the argument range, allowing 26-rc8-mm1 to boot on this
platform.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@...com>

 mm/bootmem.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6.26-rc8-mm1/mm/bootmem.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/mm/bootmem.c	2008-07-09 16:11:23.000000000 -0400
+++ linux-2.6.26-rc8-mm1/mm/bootmem.c	2008-07-09 16:13:46.000000000 -0400
@@ -299,7 +299,8 @@ static int __init mark_bootmem(unsigned 
 		int err;
 		unsigned long max;

-		if (pos < bdata->node_min_pfn) {
+		if (pos < bdata->node_min_pfn ||
+		    pos >= bdata->node_low_pfn) {
 			BUG_ON(pos != start);
 			continue;
 		}

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