[PATCH 3.16.y-ckt 022/216] Drivers: hv: vmbus: Fix a race condition when unregistering a device

Luis Henriques
2015-01-12T18:05:42Z

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 04a258c162a85c0f4ae56be67634dc43c9a4fa9b upstream.

When build with Debug the following crash is sometimes observed:
Call Trace:
[<ffffffff812b9600>] string+0x40/0x100
[<ffffffff812bb038>] vsnprintf+0x218/0x5e0
[<ffffffff810baf7d>] ? trace_hardirqs_off+0xd/0x10
[<ffffffff812bb4c1>] vscnprintf+0x11/0x30
[<ffffffff8107a2f0>] vprintk+0xd0/0x5c0
[<ffffffffa0051ea0>] ? vmbus_process_rescind_offer+0x0/0x110 [hv_vmbus]
[<ffffffff8155c71c>] printk+0x41/0x45
[<ffffffffa004ebac>] vmbus_device_unregister+0x2c/0x40 [hv_vmbus]
[<ffffffffa0051ecb>] vmbus_process_rescind_offer+0x2b/0x110 [hv_vmbus]
...

This happens due to the following race: between 'if (channel->device_obj)' check
in vmbus_process_rescind_offer() and pr_debug() in vmbus_device_unregister() the
device can disappear. Fix the issue by taking an additional reference to the
device before proceeding to vmbus_device_unregister().

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
drivers/hv/channel_mgmt.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index ed9350d42764..75330b3e388e 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -216,9 +216,16 @@ static void vmbus_process_rescind_offer(struct work_struct *work)
unsigned long flags;
struct vmbus_channel *primary_channel;
struct vmbus_channel_relid_released msg;
+ struct device *dev;
+
+ if (channel->device_obj) {
+ dev = get_device(&channel->device_obj->device);
+ if (dev) {
+ vmbus_device_unregister(channel->device_obj);
+ put_device(dev);
+ }
+ }

- if (channel->device_obj)
- vmbus_device_unregister(channel->device_obj);
memset(&msg, 0, sizeof(struct vmbus_channel_relid_released));
msg.child_relid = channel->offermsg.child_relid;
msg.header.msgtype = CHANNELMSG_RELID_RELEASED;
--
2.1.4