From: Laura Abbott <laura@xxxxxxxxxxxx> 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) [<c0218280>] (unwind_backtrace) from [<c0212be8>] (show_stack+0x20/0x24) [<c0212be8>] (show_stack) from [<c0af7124>] (dump_stack+0x80/0x9c) [<c0af7124>] (dump_stack) from [<c0301570>] (bad_page+0xc8/0x128) [<c0301570>] (bad_page) from [<c03018a8>] (free_pages_prepare+0x168/0x1e0) [<c03018a8>] (free_pages_prepare) from [<c030369c>] (free_hot_cold_page+0x3c/0x174) [<c030369c>] (free_hot_cold_page) from [<c0303828>] (__free_pages+0x54/0x58) [<c0303828>] (__free_pages) from [<c030395c>] (free_highmem_page+0x38/0x88) [<c030395c>] (free_highmem_page) from [<c0f62d5c>] (mem_init+0x240/0x430) [<c0f62d5c>] (mem_init) from [<c0f5db3c>] (start_kernel+0x1e4/0x3c8) [<c0f5db3c>] (start_kernel) from [<80208074>] (0x80208074) Disabling lock debugging due to kernel taint Removing the lower 2MB made the start of the lowmem zone to no longer be page block aligned. IFC6410 uses CONFIG_FLATMEM where alloc_node_mem_map allocates memory for the mem_map. alloc_node_mem_map will offset for unaligned nodes with the assumption the pfn/page translation functions will account for the offset. The functions for CONFIG_FLATMEM do not offset however, resulting in overrunning the memmap array. Just use the allocated memmap without any offset when running with CONFIG_FLATMEM to avoid the overrun. Signed-off-by: Laura Abbott <laura@xxxxxxxxxxxx> Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx> Reported-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> Tested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Tested-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxx> --- I was reminded at Linaro Connect that I never followed up on this patch. v3 (http://marc.info/?l=linux-mm&m=142629173021316&w=2) was dropped due to crashing (https://lkml.org/lkml/2015/3/20/546) The fundamentals of the patch were fine, the VM_BUG_ON I added turned out to be incorrect. It was supposed to be a sanity check but it didn't actually hold true in all cases (or even most cases...) v4 just drops the sanity check. I verified that the offset is working on both ARM, x86, and i386 QEMU with the config provided by Steven Rostedt. Since this was minor diff from the previous patch, I kept all the previous Acked-by/Tested-by. --- mm/page_alloc.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 40e2942..9e5ba5e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4953,6 +4953,8 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) { + unsigned long __maybe_unused offset = 0; + /* Skip empty nodes */ if (!pgdat->node_spanned_pages) return; @@ -4969,6 +4971,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) * for the buddy allocator to function correctly. */ start = pgdat->node_start_pfn & ~(MAX_ORDER_NR_PAGES - 1); + offset = pgdat->node_start_pfn - start; end = pgdat_end_pfn(pgdat); end = ALIGN(end, MAX_ORDER_NR_PAGES); size = (end - start) * sizeof(struct page); @@ -4976,7 +4979,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) if (!map) map = memblock_virt_alloc_node_nopanic(size, pgdat->node_id); - pgdat->node_mem_map = map + (pgdat->node_start_pfn - start); + pgdat->node_mem_map = map + offset; } #ifndef CONFIG_NEED_MULTIPLE_NODES /* @@ -4984,9 +4987,9 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) */ if (pgdat == NODE_DATA(0)) { mem_map = NODE_DATA(0)->node_mem_map; -#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP +#if defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) || defined(CONFIG_FLATMEM) if (page_to_pfn(mem_map) != pgdat->node_start_pfn) - mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET); + mem_map -= offset; #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */ } #endif -- 2.4.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>