powercap: intel_rapl: add NULL pointer check to rapl_mmio_cpu_online()

RAPL MMIO support depends on the RAPL common driver.  During CPU
initialization rapl_mmio_cpu_online() is called via CPU hotplug
to initialize the MMIO RAPL for the new CPU, but if that CPU is
not present in the common RAPL driver's support list, rapl_defaults
is NULL and the kernel crashes on an attempt to dereference it:

[    4.188566] BUG: kernel NULL pointer dereference, address: 0000000000000020
...snip...
[    4.189555] RIP: 0010:rapl_add_package+0x223/0x574
[    4.189555] Code: b5 a0 31 c0 49 8b 4d 78 48 01 d9 48 8b 0c c1 49 89 4c c6 10 48 ff c0 48 83 f8 05 75 e7 49 83 ff 03 75 15 48 8b 05 09 bc 18 01 <8b> 70 20 41 89 b6 0c 05 00 00 85 f6 75 1a 49 81 c6 18 9
[    4.189555] RSP: 0000:ffffb3adc00b3d90 EFLAGS: 00010246
[    4.189555] RAX: 0000000000000000 RBX: 0000000000000098 RCX: 0000000000000000
[    4.267161] usb 1-1: New USB device found, idVendor=2109, idProduct=2812, bcdDevice= b.e0
[    4.189555] RDX: 0000000000001000 RSI: 0000000000000000 RDI: ffff9340caafd000
[    4.189555] RBP: ffffb3adc00b3df8 R08: ffffffffa0246e28 R09: ffff9340caafc000
[    4.189555] R10: 000000000000024a R11: ffffffff9ff1f6f2 R12: 00000000ffffffed
[    4.189555] R13: ffff9340caa94800 R14: ffff9340caafc518 R15: 0000000000000003
[    4.189555] FS:  0000000000000000(0000) GS:ffff9340ce200000(0000) knlGS:0000000000000000
[    4.189555] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.189555] CR2: 0000000000000020 CR3: 0000000302c14001 CR4: 00000000003606f0
[    4.189555] Call Trace:
[    4.189555]  ? __switch_to_asm+0x40/0x70
[    4.189555]  rapl_mmio_cpu_online+0x47/0x64
[    4.189555]  ? rapl_mmio_write_raw+0x33/0x33
[    4.281059] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[    4.189555]  cpuhp_invoke_callback+0x29f/0x66f
[    4.189555]  ? __schedule+0x46d/0x6a0
[    4.189555]  cpuhp_thread_fun+0xb9/0x11c
[    4.189555]  smpboot_thread_fn+0x17d/0x22f
[    4.297006] usb 1-1: Product: USB2.0 Hub
[    4.189555]  ? cpu_report_death+0x43/0x43
[    4.189555]  kthread+0x137/0x13f
[    4.189555]  ? cpu_report_death+0x43/0x43
[    4.189555]  ? kthread_blkcg+0x2e/0x2e
[    4.312951] usb 1-1: Manufacturer: VIA Labs, Inc.
[    4.189555]  ret_from_fork+0x1f/0x40
[    4.189555] Modules linked in:
[    4.189555] CR2: 0000000000000020
[    4.189555] ---[ end trace 01bb812aabc791f4 ]---

To avoid that problem, check rapl_defaults NULL upfront and return an
error code if it is NULL.  [Note that it does not make sense to even
try to allocate memory in that case, because it is not going to be
used anyway.]

Fixes: 555c45fe ("int340X/processor_thermal_device: add support for MMIO RAPL")
Cc: 5.3+ <stable@vger.kernel.org> # 5.3+
Signed-off-by: Harry Pan <harry.pan@intel.com>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/powercap/intel_rapl_common.c

@@ -1295,6 +1295,9 @@ struct rapl_package *rapl_add_package(int cpu, struct rapl_if_priv *priv)
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 	int ret;
 
+	if (!rapl_defaults)
+		return ERR_PTR(-ENODEV);
+
 	rp = kzalloc(sizeof(struct rapl_package), GFP_KERNEL);
 	if (!rp)
 		return ERR_PTR(-ENOMEM);