kmemleak-test: add percpu leak

Add a per-CPU memory leak, which will be reported like:

unreferenced object 0x3efa840195f8 (size 64):
comm "modprobe", pid 4667, jiffies 4294688677
hex dump (first 32 bytes on cpu 0):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 0):
[<ffffffffa7fa87af>] pcpu_alloc+0x3df/0x840
[<ffffffffc11642d9>] kmemleak_test_init+0x2c9/0x2f0 [kmemleak_test]
[<ffffffffa7c02264>] do_one_initcall+0x44/0x300
[<ffffffffa7de9e10>] do_init_module+0x60/0x240
[<ffffffffa7deb946>] init_module_from_file+0x86/0xc0
[<ffffffffa7deba99>] idempotent_init_module+0x109/0x2a0
[<ffffffffa7debd2a>] __x64_sys_finit_module+0x5a/0xb0
[<ffffffffa88f4f3a>] do_syscall_64+0x7a/0x160
[<ffffffffa8a0012b>] entry_SYSCALL_64_after_hwframe+0x76/0x7e

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Pavel Tikhomirov <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Cc: Alexander Mikhalitsyn <[e-mail]>
Cc: Chen Jun <[e-mail]>
Cc: Wei Yongjun <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

samples/kmemleak/kmemleak-test.c

···
 			per_cpu(kmemleak_test_pointer, i));
 	}
 
+	pr_info("__alloc_percpu(64, 4) = %p\n", __alloc_percpu(64, 4));
+
 	return 0;
 }
 module_init(kmemleak_test_init);