Revert "mm,memblock: reset memblock.reserved to system init state to prevent UAF"

This reverts commit 9e46e4d.

kbuild reports a warning in memblock_remove_region() because of a false
positive caused by partial reset of the memblock state.

Doing the full reset will remove the false positives, but will allow
late use of memblock_free() to go unnoticed, so it is better to revert
the offending commit.

   WARNING: CPU: 0 PID: 1 at mm/memblock.c:352 memblock_remove_region (kbuild/src/x86_64/mm/memblock.c:352 (discriminator 1))
   Modules linked in:
   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc3-00001-g9e46e4dcd9d6 #2
   RIP: 0010:memblock_remove_region (kbuild/src/x86_64/mm/memblock.c:352 (discriminator 1))
   Call Trace:
     memblock_discard (kbuild/src/x86_64/mm/memblock.c:383)
     page_alloc_init_late (kbuild/src/x86_64/include/linux/find.h:208 kbuild/src/x86_64/include/linux/nodemask.h:266 kbuild/src/x86_64/mm/mm_init.c:2405)
     kernel_init_freeable (kbuild/src/x86_64/init/main.c:1325 kbuild/src/x86_64/init/main.c:1546)
     kernel_init (kbuild/src/x86_64/init/main.c:1439)
     ret_from_fork (kbuild/src/x86_64/arch/x86/kernel/process.c:145)
     ret_from_fork_asm (kbuild/src/x86_64/arch/x86/entry/entry_64.S:298)

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: "Mike Rapoport (IBM)" <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: rppt

mm/memblock.c

@@ -374,10 +374,6 @@ void __init memblock_discard(void)
 			kfree(memblock.reserved.regions);
 		else
 			memblock_free_late(addr, size);
-		/* Reset to prevent UAF from stray frees. */
-		memblock.reserved.regions = memblock_reserved_init_regions;
-		memblock.reserved.cnt = 1;
-		memblock_remove_region(&memblock.reserved, 0);
 	}
 
 	if (memblock.memory.regions != memblock_memory_init_regions) {