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Commit 04a258c1 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Greg Kroah-Hartman
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Drivers: hv: vmbus: Fix a race condition when unregistering a device 



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: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 31d4ea1a

drivers/hv/channel_mgmt.c

+9 −2
Original line number Diff line number Diff line
@@ -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)

	if (channel->device_obj) {

		dev = get_device(&channel->device_obj->device);

		if (dev) {

			vmbus_device_unregister(channel->device_obj);

			put_device(dev);

		}

	}



	memset(&msg, 0, sizeof(struct vmbus_channel_relid_released));

	msg.child_relid = channel->offermsg.child_relid;

	msg.header.msgtype = CHANNELMSG_RELID_RELEASED;