This patch fixes the race between netvsc_probe() and
rndis_set_subchannel(), which can cause a deadlock.
Fixes: 8195b1396ec8 ("hv_netvsc: fix deadlock on hotplug")
Signed-off-by: Dexuan Cui <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: Haiyang Zhang <[email protected]>
---
drivers/net/hyperv/netvsc_drv.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
FYI: these are the related 3 paths which show the deadlock:
#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
#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
#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.
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 1121a1ec..4fd14a0 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -2206,6 +2206,16 @@ static int netvsc_probe(struct hv_device *dev,
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);
@@ -2224,7 +2234,6 @@ static int netvsc_probe(struct hv_device *dev,
else
net->max_mtu = ETH_DATA_LEN;
- rtnl_lock();
ret = register_netdevice(net);
if (ret != 0) {
pr_err("Unable to register netdev.\n");
--
2.7.4
From: Dexuan Cui <[email protected]>
Date: Wed, 22 Aug 2018 21:20:03 +0000
> ---
> drivers/net/hyperv/netvsc_drv.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
>
> FYI: these are the related 3 paths which show the deadlock:
This incredibly useful information belongs in the commit log
message, and therefore before the --- and signoffs.
> From: David Miller <[email protected]>
> Sent: Wednesday, August 29, 2018 17:49
>
> From: Dexuan Cui <[email protected]>
> Date: Wed, 22 Aug 2018 21:20:03 +0000
>
> > ---
> > drivers/net/hyperv/netvsc_drv.c | 11 ++++++++++-
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> >
> > FYI: these are the related 3 paths which show the deadlock:
>
> This incredibly useful information belongs in the commit log
> message, and therefore before the --- and signoffs.
Hi David,
I was afraid the call-traces are too detailed. :-)
Can you please move the info to before the --- line?
Or, should I resend the patch with the commit log updated?
Thanks,
-- Dexuan
From: Dexuan Cui <[email protected]>
Date: Thu, 30 Aug 2018 00:58:48 +0000
>> From: David Miller <[email protected]>
>> Sent: Wednesday, August 29, 2018 17:49
>>
>> From: Dexuan Cui <[email protected]>
>> Date: Wed, 22 Aug 2018 21:20:03 +0000
>>
>> > ---
>> > drivers/net/hyperv/netvsc_drv.c | 11 ++++++++++-
>> > 1 file changed, 10 insertions(+), 1 deletion(-)
>> >
>> >
>> > FYI: these are the related 3 paths which show the deadlock:
>>
>> This incredibly useful information belongs in the commit log
>> message, and therefore before the --- and signoffs.
>
> Hi David,
> I was afraid the call-traces are too detailed. :-)
>
> Can you please move the info to before the --- line?
>
> Or, should I resend the patch with the commit log updated?
Please resend.
> From: David Miller <[email protected]>
> Sent: Wednesday, August 29, 2018 19:09
> > Hi David,
> > I was afraid the call-traces are too detailed. :-)
> >
> > Can you please move the info to before the --- line?
> >
> > Or, should I resend the patch with the commit log updated?
>
> Please resend.
OK. Will do.
-- Dexuan