[PATCH] hv: Don't OOPS when can't init vmbus

[Sasha Levin <levinsasha928@gmail.com>]

The hv vmbus driver was causing an OOPS since it was trying to register drivers
on top of the bus even if initialization of the bus has failed for some
reason (such as the odd chance someone would run a hv enabled kernel in a
non-hv environment).

The following OOPS was happening:

[    2.822634] kernel BUG at drivers/base/driver.c:227!
[    2.822734] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[    2.822734] CPU 0
[    2.822734] Pid: 1, comm: swapper Not tainted 3.2.0-rc2-sasha-00146-gc729049-dirty #13
[    2.822734] RIP: 0010:[<ffffffff81769563>]  [<ffffffff81769563>] driver_register+0x1f/0x104
[    2.822734] RSP: 0018:ffff880012499e00  EFLAGS: 00010246
[    2.822734] RAX: ffffffff822f9fc0 RBX: ffffffff822fa5e0 RCX: 0000000046494648
[    2.822734] RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff822fa5e0
[    2.822734] RBP: ffff880012499e30 R08: 0000000000000002 R09: ffffffff8221ab98
[    2.822734] R10: ffff880012499c20 R11: 0000000000000000 R12: 0000000000000000
[    2.822734] R13: ffffffff81ff810a R14: 0000000000000000 R15: 0000000000000000
[    2.822734] FS:  0000000000000000(0000) GS:ffff880013a00000(0000) knlGS:0000000000000000
[    2.822734] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    2.822734] CR2: 0000000000000000 CR3: 0000000002205000 CR4: 00000000000406f0
[    2.822734] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    2.822734] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[    2.822734] Process swapper (pid: 1, threadinfo ffff880012498000, task ffff880012490000)
[    2.822734] Stack:
[    2.822734]  ffff880012499e60 ffffffff822fa5c0 0000000000000000 ffffffff81ff810a
[    2.822734]  0000000000000000 0000000000000000 ffff880012499e60 ffffffff8190f991
[    2.822734]  ffffffff83388110 ffffffff8274d4a8 ffffffff8269a649 0000000000000000
[    2.822734] Call Trace:
[    2.822734]  [<ffffffff8190f991>] __vmbus_driver_register+0x47/0x59
[    2.822734]  [<ffffffff8269a649>] ? hv_acpi_init+0x199/0x199
[    2.822734]  [<ffffffff8269a670>] init_hyperv_utils+0x27/0x29
[    2.822734]  [<ffffffff82656c02>] do_one_initcall+0x7a/0x135
[    2.822734]  [<ffffffff82656da7>] kernel_init+0xea/0x16f
[    2.822734]  [<ffffffff81b99144>] kernel_thread_helper+0x4/0x10
[    2.822734]  [<ffffffff81b966b8>] ? retint_restore_args+0x13/0x13
[    2.822734]  [<ffffffff82656cbd>] ? do_one_initcall+0x135/0x135
[    2.822734]  [<ffffffff81b99140>] ? gs_change+0x13/0x13
[    2.822734] Code: d2 74 07 48 8b 82 d0 00 00 00 c9 c3 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 89 fb 48 83 ec 08 48 8b 47 08 48 83 78 68 00 75 02 <0f> 0b 48 83 78 30 00 74 07 48 83 7f 30 00 75 1c 48 83 78 38 00
[    2.822734] RIP  [<ffffffff81769563>] driver_register+0x1f/0x104
[    2.822734]  RSP <ffff880012499e00>

Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---

btw, It would be nice if it could also get a MAINTAINERS entry.

I'm pretty sure Greg isn't the maintainer, but his name was on
top of the commit signers.

 drivers/hv/vmbus_drv.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 0c048dd..d3b0b4f 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -62,6 +62,14 @@ struct hv_device_info {
 	struct hv_dev_port_info outbound;
 };
 
+static int vmbus_exists(void)
+{
+	if (hv_acpi_dev == NULL)
+		return -ENODEV;
+
+	return 0;
+}
+
 
 static void get_channel_info(struct hv_device *device,
 			     struct hv_device_info *info)
@@ -590,6 +598,10 @@ int __vmbus_driver_register(struct hv_driver *hv_driver, struct module *owner, c
 
 	pr_info("registering driver %s\n", hv_driver->name);
 
+	ret = vmbus_exists();
+	if (ret < 0)
+		return ret;
+
 	hv_driver->driver.name = hv_driver->name;
 	hv_driver->driver.owner = owner;
 	hv_driver->driver.mod_name = mod_name;
@@ -614,6 +626,9 @@ void vmbus_driver_unregister(struct hv_driver *hv_driver)
 {
 	pr_info("unregistering driver %s\n", hv_driver->name);
 
+	if (!vmbus_exists())
+		return;
+
 	driver_unregister(&hv_driver->driver);
 
 }
@@ -776,6 +791,7 @@ static int __init hv_acpi_init(void)
 
 cleanup:
 	acpi_bus_unregister_driver(&vmbus_acpi_driver);
+	hv_acpi_dev = NULL;
 	return ret;
 }
 
-- 
1.7.8.rc1