x86/setup: Fix static memory detection

When booting x86 images in qemu, the following warning is seen randomly
if DEBUG_LOCKDEP is enabled.

  WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:1119
	  lockdep_register_key+0xc0/0x100

static_obj() returns true if an address is between _stext and _end.

On x86, this includes the brk memory space. Problem is that this memory
block is not static on x86; its unused portions are released after init
and can be allocated. This results in the observed warning if a lockdep
object is allocated from this memory.

Solve the problem by implementing arch_is_kernel_initmem_freed() for
x86 and have it return true if an address is within the released memory
range.

The same problem was solved for s390 with commit

  7a5da02d ("locking/lockdep: check for freed initmem in static_obj()"),

which introduced arch_is_kernel_initmem_freed().
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200131021159.9178-1-linux@roeck-us.net

arch/x86/include/asm/sections.h

@@ -2,6 +2,8 @@
 #ifndef _ASM_X86_SECTIONS_H
 #define _ASM_X86_SECTIONS_H
 
+#define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
+
 #include <asm-generic/sections.h>
 #include <asm/extable.h>
 
@@ -14,4 +16,22 @@ extern char __end_rodata_hpage_align[];
 
 extern char __end_of_kernel_reserve[];
 
+extern unsigned long _brk_start, _brk_end;
+
+static inline bool arch_is_kernel_initmem_freed(unsigned long addr)
+{
+	/*
+	 * If _brk_start has not been cleared, brk allocation is incomplete,
+	 * and we can not make assumptions about its use.
+	 */
+	if (_brk_start)
+		return 0;
+
+	/*
+	 * After brk allocation is complete, space between _brk_end and _end
+	 * is available for allocation.
+	 */
+	return addr >= _brk_end && addr < (unsigned long)&_end;
+}
+
 #endif	/* _ASM_X86_SECTIONS_H */

arch/x86/kernel/setup.c

@@ -64,7 +64,6 @@ RESERVE_BRK(dmi_alloc, 65536);
  * at link time, with RESERVE_BRK*() facility reserving additional
  * chunks.
  */
-static __initdata
 unsigned long _brk_start = (unsigned long)__brk_base;
 unsigned long _brk_end   = (unsigned long)__brk_base;