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: 8195b1396e ("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>
e04e7a7bbd