EDAC, mc_sysfs: Fix freeing bus' name

I get the splat below when modprobing/rmmoding EDAC drivers. It happens
because bus->name is invalid after bus_unregister() has run. The Code: section
below corresponds to:

  .loc 1 1108 0
  movq    672(%rbx), %rax # mci_1(D)->bus, mci_1(D)->bus
  .loc 1 1109 0
  popq    %rbx    #

  .loc 1 1108 0
  movq    (%rax), %rdi    # _7->name,
  jmp     kfree   #

and %rax has some funky stuff 2030203020312030 which looks a lot like
something walked over it.

Fix that by saving the name ptr before doing stuff to string it points to.

  general protection fault: 0000 [#1] SMP
  Modules linked in: ...
  CPU: 4 PID: 10318 Comm: modprobe Tainted: G          I EN  3.12.51-11-default+ #48
  Hardware name: HP ProLiant DL380 G7, BIOS P67 05/05/2011
  task: ffff880311320280 ti: ffff88030da3e000 task.ti: ffff88030da3e000
  RIP: 0010:[<ffffffffa019da92>]  [<ffffffffa019da92>] edac_unregister_sysfs+0x22/0x30 [edac_core]
  RSP: 0018:ffff88030da3fe28  EFLAGS: 00010292
  RAX: 2030203020312030 RBX: ffff880311b4e000 RCX: 000000000000095c
  RDX: 0000000000000001 RSI: ffff880327bb9600 RDI: 0000000000000286
  RBP: ffff880311b4e750 R08: 0000000000000000 R09: ffffffff81296110
  R10: 0000000000000400 R11: 0000000000000000 R12: ffff88030ba1ac68
  R13: 0000000000000001 R14: 00000000011b02f0 R15: 0000000000000000
  FS:  00007fc9bf8f5700(0000) GS:ffff8801a7c40000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  CR2: 0000000000403c90 CR3: 000000019ebdf000 CR4: 00000000000007e0
  Stack:
  Call Trace:
    i7core_unregister_mci.isra.9
    i7core_remove
    pci_device_remove
    __device_release_driver
    driver_detach
    bus_remove_driver
    pci_unregister_driver
    i7core_exit
    SyS_delete_module
    system_call_fastpath
    0x7fc9bf426536
  Code: 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 53 48 89 fb e8 52 2a 1f e1 48 8b bb a0 02 00 00 e8 46 59 1f e1 48 8b 83 a0 02 00 00 5b <48> 8b 38 e9 26 9a fe e0 66 0f 1f 44 00 00 66 66 66 66 90 48 8b
  RIP  [<ffffffffa019da92>] edac_unregister_sysfs+0x22/0x30 [edac_core]
   RSP <ffff88030da3fe28>

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: <stable@vger.kernel.org> # v3.6..
Fixes: 7a623c039075 ("edac: rewrite the sysfs code to use struct device")

drivers/edac/edac_mc_sysfs.c

@@ -880,21 +880,26 @@ static struct device_type mci_attr_type = {
 int edac_create_sysfs_mci_device(struct mem_ctl_info *mci,
 				 const struct attribute_group **groups)
 {
+	char *name;
 	int i, err;
 
 	/*
 	 * The memory controller needs its own bus, in order to avoid
 	 * namespace conflicts at /sys/bus/edac.
 	 */
-	mci->bus->name = kasprintf(GFP_KERNEL, "mc%d", mci->mc_idx);
-	if (!mci->bus->name)
+	name = kasprintf(GFP_KERNEL, "mc%d", mci->mc_idx);
+	if (!name)
 		return -ENOMEM;
 
+	mci->bus->name = name;
+
 	edac_dbg(0, "creating bus %s\n", mci->bus->name);
 
 	err = bus_register(mci->bus);
-	if (err < 0)
-		goto fail_free_name;
+	if (err < 0) {
+		kfree(name);
+		return err;
+	}
 
 	/* get the /sys/devices/system/edac subsys reference */
 	mci->dev.type = &mci_attr_type;
@@ -961,8 +966,8 @@ fail_unregister_dimm:
 	device_unregister(&mci->dev);
 fail_unregister_bus:
 	bus_unregister(mci->bus);
-fail_free_name:
-	kfree(mci->bus->name);
+	kfree(name);
+
 	return err;
 }
 
@@ -993,10 +998,12 @@ void edac_remove_sysfs_mci_device(struct mem_ctl_info *mci)
 
 void edac_unregister_sysfs(struct mem_ctl_info *mci)
 {
+	const char *name = mci->bus->name;
+
 	edac_dbg(1, "Unregistering device %s\n", dev_name(&mci->dev));
 	device_unregister(&mci->dev);
 	bus_unregister(mci->bus);
-	kfree(mci->bus->name);
+	kfree(name);
 }
 
 static void mc_attr_release(struct device *dev)