Commit 55878e88 authored by Cody P Schafer's avatar Cody P Schafer Committed by Linus Torvalds
Browse files

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
	"sparsemem: fix boot when SECTIONS_PER_ROOT is not power-of-2"

Signed-off-by: default avatarCody P Schafer <>
Acked-by: default avatarDave Hansen <>
Cc: Jiang Liu <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent b26a3dfd
...@@ -1137,6 +1137,10 @@ struct mem_section { ...@@ -1137,6 +1137,10 @@ struct mem_section {
struct page_cgroup *page_cgroup; struct page_cgroup *page_cgroup;
unsigned long pad; unsigned long pad;
#endif #endif
* WARNING: mem_section must be a power-of-2 in size for the
* calculation and use of SECTION_ROOT_MASK to make sense.
}; };
...@@ -481,6 +481,9 @@ void __init sparse_init(void) ...@@ -481,6 +481,9 @@ void __init sparse_init(void)
struct page **map_map; struct page **map_map;
#endif #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 */ /* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
set_pageblock_order(); set_pageblock_order();
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