From 04a258c162a85c0f4ae56be67634dc43c9a4fa9b Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Tue, 4 Nov 2014 13:40:11 +0100 Subject: [PATCH] Drivers: hv: vmbus: Fix a race condition when unregistering a device When build with Debug the following crash is sometimes observed: Call Trace: [] string+0x40/0x100 [] vsnprintf+0x218/0x5e0 [] ? trace_hardirqs_off+0xd/0x10 [] vscnprintf+0x11/0x30 [] vprintk+0xd0/0x5c0 [] ? vmbus_process_rescind_offer+0x0/0x110 [hv_vmbus] [] printk+0x41/0x45 [] vmbus_device_unregister+0x2c/0x40 [hv_vmbus] [] 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 Signed-off-by: K. Y. Srinivasan Cc: Signed-off-by: Greg Kroah-Hartman --- 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 a2d1a9612c86..d36ce6835fb7 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; -- 2.39.5