ACPI / device_sysfs: Avoid OF modalias creation for removed device

If SSDT overlay is loaded via ConfigFS and then unloaded the device,
we would like to have OF modalias for, already gone. Thus, acpi_get_name()
returns no allocated buffer for such case and kernel crashes afterwards:

 ACPI: Host-directed Dynamic ACPI Table Unload
 ads7950 spi-PRP0001:00: Dropping the link to regulator.0
 BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
 #PF error: [normal kernel read fault]
 PGD 80000000070d6067 P4D 80000000070d6067 PUD 70d0067 PMD 0
 Oops: 0000 [#1] SMP PTI
 CPU: 0 PID: 40 Comm: kworker/u4:2 Not tainted 5.0.0+ #96
 Hardware name: Intel Corporation Merrifield/BODEGA BAY, BIOS 542 2015.01.21:18.19.48
 Workqueue: kacpi_hotplug acpi_device_del_work_fn
 RIP: 0010:create_of_modalias.isra.1+0x4c/0x150
 Code: 00 00 48 89 44 24 18 31 c0 48 8d 54 24 08 48 c7 44 24 10 00 00 00 00 48 c7 44 24 08 ff ff ff ff e8 7a b0 03 00 48 8b 4c 24 10 <0f> b6 01 84 c0 74 27 48 c7 c7 00 09 f4 a5 0f b6 f0 8d 50 20 f6 04
 RSP: 0000:ffffa51040297c10 EFLAGS: 00010246
 RAX: 0000000000001001 RBX: 0000000000000785 RCX: 0000000000000000
 RDX: 0000000000001001 RSI: 0000000000000286 RDI: ffffa2163dc042e0
 RBP: ffffa216062b1196 R08: 0000000000001001 R09: ffffa21639873000
 R10: ffffffffa606761d R11: 0000000000000001 R12: ffffa21639873218
 R13: ffffa2163deb5060 R14: ffffa216063d1010 R15: 0000000000000000
 FS:  0000000000000000(0000) GS:ffffa2163e000000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 0000000007114000 CR4: 00000000001006f0
 Call Trace:
  __acpi_device_uevent_modalias+0xb0/0x100
  spi_uevent+0xd/0x40

 ...

In order to fix above let create_of_modalias() check the status returned
by acpi_get_name() and bail out in case of failure.

Fixes: 8765c5b ("ACPI / scan: Rework modalias creation when "compatible" is present")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=201381
Reported-by: Ferry Toth <fntoth@gmail.com>
Tested-by: Ferry Toth<fntoth@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: 4.1+ <stable@vger.kernel.org> # 4.1+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/device_sysfs.c

@@ -202,11 +202,15 @@ static int create_of_modalias(struct acpi_device *acpi_dev, char *modalias,
 {
 	struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER };
 	const union acpi_object *of_compatible, *obj;
+	acpi_status status;
 	int len, count;
 	int i, nval;
 	char *c;
 
-	acpi_get_name(acpi_dev->handle, ACPI_SINGLE_NAME, &buf);
+	status = acpi_get_name(acpi_dev->handle, ACPI_SINGLE_NAME, &buf);
+	if (ACPI_FAILURE(status))
+		return -ENODEV;
+
 	/* DT strings are all in lower case */
 	for (c = buf.pointer; *c != '\0'; c++)
 		*c = tolower(*c);