Commit b6da0ffb authored May 30, 2010 by Kevin Cernekee Committed by Ralf Baechle Jul 25, 2011

MIPS: pfn_valid() is broken on low memory HIGHMEM systems



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>
To: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1992/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

parent e36863a5

arch/mips/mm/init.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -368,7 +368,7 @@ void __init mem_init(void)
	#ifdef CONFIG_DISCONTIGMEM		#ifdef CONFIG_DISCONTIGMEM
	#error "CONFIG_HIGHMEM and CONFIG_DISCONTIGMEM dont work together yet"		#error "CONFIG_HIGHMEM and CONFIG_DISCONTIGMEM dont work together yet"
	#endif		#endif
	max_mapnr = highend_pfn;		max_mapnr = highend_pfn ? highend_pfn : max_low_pfn;
	#else		#else
	max_mapnr = max_low_pfn;		max_mapnr = max_low_pfn;
	#endif		#endif