[PATCH resend 6/9] MIPS: pfn_valid() is broken on low memory HIGHMEM systems

Kevin Cernekee
2010-10-16T21:44:57Z

pfn_valid() compares the PFN to max_mapnr:

__pfn >= min_low_pfn && __pfn < max_mapnr;

On HIGHMEM kernels, highend_pfn is used to set the value of max_mapnr.
Unfortunately, highend_pfn is left at zero if the system does not
actually have enough RAM to reach into the HIGHMEM range. This causes
pfn_valid() to always return false, and when debug checks are enabled
the kernel will fail catastrophically:

Memory: 22432k/32768k available (2249k kernel code, 10336k reserved, 653k data, 1352k init, 0k highmem)
NR_IRQS:128
kfree_debugcheck: out of range ptr 81c02900h.
Kernel bug detected[#1]:
Cpu 0
$ 0 : 00000000 10008400 00000034 00000000
$ 4 : 8003e160 802a0000 8003e160 00000000
$ 8 : 00000000 0000003e 00000747 00000747
...

On such a configuration, max_low_pfn should be used to set max_mapnr.

This was seen on 2.6.34.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
---
arch/mips/mm/init.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 2efcbd2..18183a4 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -370,7 +370,7 @@ void __init mem_init(void)
#ifdef CONFIG_DISCONTIGMEM
#error "CONFIG_HIGHMEM and CONFIG_DISCONTIGMEM dont work together yet"
#endif
- max_mapnr = highend_pfn;
+ max_mapnr = highend_pfn ? : max_low_pfn;
#else
max_mapnr = max_low_pfn;
#endif
--
1.7.0.4