OpenWrt – Rev 1
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From: Tobias Wolf <dev-NTEO@vplace.de>
Subject: mm: Fix alloc_node_mem_map with ARCH_PFN_OFFSET calculation
An rt288x (ralink) based router (Belkin F5D8235 v1) does not boot with any
kernel beyond version 4.3 resulting in:
BUG: Bad page state in process swapper pfn:086ac
bisect resulted in:
a1c34a3bf00af2cede839879502e12dc68491ad5 is the first bad commit
commit a1c34a3bf00af2cede839879502e12dc68491ad5
Author: Laura Abbott <laura@labbott.name>
Date: Thu Nov 5 18:48:46 2015 -0800
mm: Don't offset memmap for flatmem
Srinivas Kandagatla reported bad page messages when trying to remove the
bottom 2MB on an ARM based IFC6410 board
BUG: Bad page state in process swapper pfn:fffa8
page:ef7fb500 count:0 mapcount:0 mapping: (null) index:0x0
flags: 0x96640253(locked|error|dirty|active|arch_1|reclaim|mlocked)
page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
bad because of flags:
flags: 0x200041(locked|active|mlocked)
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00007-g412f9ba-dirty
#816
Hardware name: Qualcomm (Flattened Device Tree)
unwind_backtrace
show_stack
dump_stack
bad_page
free_pages_prepare
free_hot_cold_page
__free_pages
free_highmem_page
mem_init
start_kernel
Disabling lock debugging due to kernel taint
[...]
:040000 040000 2de013c372345fd471cd58f0553c9b38b0ef1cc4
0a8156f848733dfa21e16c196dfb6c0a76290709 M mm
This fix for ARM does not account ARCH_PFN_OFFSET for mem_map as later used by
page_to_pfn anymore.
The following output was generated with two hacked in printk statements:
printk("before %p vs. %p or %p\n", mem_map, mem_map - offset, mem_map -
(pgdat->node_start_pfn - ARCH_PFN_OFFSET));
if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
mem_map -= offset + (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
printk("after %p\n", mem_map);
Output:
[ 0.000000] before 8861b280 vs. 8861b280 or 8851b280
[ 0.000000] after 8851b280
As seen in the first line mem_map with subtraction of offset does not equal the
mem_map after subtraction of ARCH_PFN_OFFSET.
After adding the offset of ARCH_PFN_OFFSET as well to mem_map as the
previously calculated offset is zero for the named platform it is able to boot
4.4 and 4.9-rc7 again.
Signed-off-by: Tobias Wolf <dev-NTEO@vplace.de>
---
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6393,7 +6393,7 @@ static void __ref alloc_node_mem_map(str
mem_map = NODE_DATA(0)->node_mem_map;
#if defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) || defined(CONFIG_FLATMEM)
if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
- mem_map -= offset;
+ mem_map -= offset + (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
}
#endif