mm/memblock: debug: don't free reserved array if !ARCH_DISCARD_MEMBLOCK

Now the Nobootmem allocator will always try to free memory allocated for
reserved memory regions (free_low_memory_core_early()) without taking
into to account current memblock debugging configuration
(CONFIG_ARCH_DISCARD_MEMBLOCK and CONFIG_DEBUG_FS state).

As result if:

 - CONFIG_DEBUG_FS defined
 - CONFIG_ARCH_DISCARD_MEMBLOCK not defined;
 - reserved memory regions array have been resized during boot

then:

 - memory allocated for reserved memory regions array will be freed to
   buddy allocator;
 - debug_fs entry "sys/kernel/debug/memblock/reserved" will show garbage
   instead of state of memory reservations.  like:
   0: 0x98393bc0..0x9a393bbf
   1: 0xff120000..0xff11ffff
   2: 0x00000000..0xffffffff

Hence, do not free memory allocated for reserved memory regions if
defined(CONFIG_DEBUG_FS) && !defined(CONFIG_ARCH_DISCARD_MEMBLOCK).

Signed-off-by: Grygorii Strashko <[email protected]>
Signed-off-by: Santosh Shilimkar <[email protected]>
Reviewed-by: Tejun Heo <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Russell King <[email protected]>
Cc: Tony Lindgren <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memblock.c

@@ -269,6 +269,19 @@ phys_addr_t __init_memblock get_allocated_memblock_reserved_regions_info(
 	if (memblock.reserved.regions == memblock_reserved_init_regions)
 		return 0;
 
+	/*
+	 * Don't allow nobootmem allocator to free reserved memory regions
+	 * array if
+	 *  - CONFIG_DEBUG_FS is enabled;
+	 *  - CONFIG_ARCH_DISCARD_MEMBLOCK is not enabled;
+	 *  - reserved memory regions array have been resized during boot.
+	 * Otherwise debug_fs entry "sys/kernel/debug/memblock/reserved"
+	 * will show garbage instead of state of memory reservations.
+	 */
+	if (IS_ENABLED(CONFIG_DEBUG_FS) &&
+	    !IS_ENABLED(CONFIG_ARCH_DISCARD_MEMBLOCK))
+		return 0;
+
 	*addr = __pa(memblock.reserved.regions);
 
 	return PAGE_ALIGN(sizeof(struct memblock_region) *