4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dexuan Cui decui@microsoft.com
[ Upstream commit e04e7a7bbd4bbabef4e1a58367e5fc9b2edc3b10 ]
This patch fixes the race between netvsc_probe() and rndis_set_subchannel(), which can cause a deadlock.
These are the related 3 paths which show the deadlock:
path #1: Workqueue: hv_vmbus_con vmbus_onmessage_work [hv_vmbus] Call Trace: schedule schedule_preempt_disabled __mutex_lock __device_attach bus_probe_device device_add vmbus_device_register vmbus_onoffer vmbus_onmessage_work process_one_work worker_thread kthread ret_from_fork
path #2: schedule schedule_preempt_disabled __mutex_lock netvsc_probe vmbus_probe really_probe __driver_attach bus_for_each_dev driver_attach_async async_run_entry_fn process_one_work worker_thread kthread ret_from_fork
path #3: Workqueue: events netvsc_subchan_work [hv_netvsc] Call Trace: schedule rndis_set_subchannel netvsc_subchan_work process_one_work worker_thread kthread ret_from_fork
Before path #1 finishes, path #2 can start to run, because just before the "bus_probe_device(dev);" in device_add() in path #1, there is a line "object_uevent(&dev->kobj, KOBJ_ADD);", so systemd-udevd can immediately try to load hv_netvsc and hence path #2 can start to run.
Next, path #2 offloads the subchannal's initialization to a workqueue, i.e. path #3, so we can end up in a deadlock situation like this:
Path #2 gets the device lock, and is trying to get the rtnl lock; Path #3 gets the rtnl lock and is waiting for all the subchannel messages to be processed; Path #1 is trying to get the device lock, but since #2 is not releasing the device lock, path #1 has to sleep; since the VMBus messages are processed one by one, this means the sub-channel messages can't be procedded, so #3 has to sleep with the rtnl lock held, and finally #2 has to sleep... Now all the 3 paths are sleeping and we hit the deadlock.
With the patch, we can make sure #2 gets both the device lock and the rtnl lock together, gets its job done, and releases the locks, so #1 and #3 will not be blocked for ever.
Fixes: 8195b1396ec8 ("hv_netvsc: fix deadlock on hotplug") Signed-off-by: Dexuan Cui decui@microsoft.com Cc: Stephen Hemminger sthemmin@microsoft.com Cc: K. Y. Srinivasan kys@microsoft.com Cc: Haiyang Zhang haiyangz@microsoft.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/hyperv/netvsc_drv.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
--- a/drivers/net/hyperv/netvsc_drv.c +++ b/drivers/net/hyperv/netvsc_drv.c @@ -2101,6 +2101,16 @@ static int netvsc_probe(struct hv_device
memcpy(net->dev_addr, device_info.mac_adr, ETH_ALEN);
+ /* We must get rtnl lock before scheduling nvdev->subchan_work, + * otherwise netvsc_subchan_work() can get rtnl lock first and wait + * all subchannels to show up, but that may not happen because + * netvsc_probe() can't get rtnl lock and as a result vmbus_onoffer() + * -> ... -> device_add() -> ... -> __device_attach() can't get + * the device lock, so all the subchannels can't be processed -- + * finally netvsc_subchan_work() hangs for ever. + */ + rtnl_lock(); + if (nvdev->num_chn > 1) schedule_work(&nvdev->subchan_work);
@@ -2119,7 +2129,6 @@ static int netvsc_probe(struct hv_device else net->max_mtu = ETH_DATA_LEN;
- rtnl_lock(); ret = register_netdevice(net); if (ret != 0) { pr_err("Unable to register netdev.\n");