sparsemem: add BUILD_BUG_ON when sizeof mem_section is non-power-of-2
Instead of leaving a hidden trap for the next person who comes along and
wants to add something to mem_section, add a big fat warning about it
needing to be a power-of-2, and insert a BUILD_BUG_ON() in sparse_init()
to catch mistakes.
Right now non-power-of-2 mem_sections cause a number of WARNs at boot
(which don't clearly point to the size of mem_section as an issue), but
the system limps on (temporarily, at least).
This is based upon Dave Hansen's earlier RFC where he ran into the same
issue:
"sparsemem: fix boot when SECTIONS_PER_ROOT is not power-of-2"
http://lkml.indiana.edu/hypermail/linux/kernel/1205.2/03077.html
Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jiang Liu <liuj97@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/sparse.c b/mm/sparse.c
index 1c91f0d3..3194ec4 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -481,6 +481,9 @@
struct page **map_map;
#endif
+ /* see include/linux/mmzone.h 'struct mem_section' definition */
+ BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
+
/* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
set_pageblock_order();