| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.18 100/150] Drivers: hv: vmbus: Fix a race condition when unregistering a device | Date | Tue, 13 Jan 2015 23:22:51 -0800 |
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3.18-stable review patch. If anyone has any objections, please let me know.
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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>
--- drivers/hv/channel_mgmt.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
--- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -216,9 +216,16 @@ static void vmbus_process_rescind_offer( 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;
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