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

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@labbott.name>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Reported-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: Santosh Shilimkar <ssantosh@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Arnd Bergman <arnd@arndb.de>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Andy Gross <agross@codeaurora.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4aed338fc535..86f7d952e2cc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5421,6 +5421,8 @@ 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;
@@ -5437,6 +5439,7 @@ 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);
@@ -5444,7 +5447,7 @@ 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
         /*
@@ -5452,9 +5455,9 @@ 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