[PATCH] net/netvsc: Fix on race condition of multiple commands

[PATCH] net/netvsc: Fix on race condition of multiple commands

[Madhuker Mythri]

When multiple processes issue command requests(like: device info get
and link-status) at same-time, then we could see the command request
failures, due to race-condition of common function execution.

So, to avoid such race-condition introduced a new spin-lock to protect
the code of critical section.

Fixes: 4e9c73e96e83 ("net/netvsc: add Hyper-V network device")
Signed-off-by: Madhuker Mythri <madhukar.mythri@gmail.com>
---
 drivers/net/netvsc/hn_ethdev.c | 1 +
 drivers/net/netvsc/hn_rndis.c  | 2 ++
 drivers/net/netvsc/hn_var.h    | 1 +
 3 files changed, 4 insertions(+)

diff --git a/drivers/net/netvsc/hn_ethdev.c b/drivers/net/netvsc/hn_ethdev.c
index 6584819f4f..b525e287fa 100644
--- a/drivers/net/netvsc/hn_ethdev.c
+++ b/drivers/net/netvsc/hn_ethdev.c
@@ -1310,6 +1310,7 @@ eth_hn_dev_init(struct rte_eth_dev *eth_dev)
 	PMD_INIT_FUNC_TRACE();
 
 	rte_spinlock_init(&hv->hotadd_lock);
+	rte_spinlock_init(&hv->cmd_lock);
 	LIST_INIT(&hv->hotadd_list);
 
 	vmbus = container_of(device, struct rte_vmbus_device, device);
diff --git a/drivers/net/netvsc/hn_rndis.c b/drivers/net/netvsc/hn_rndis.c
index 7c54eebcef..8a0716df89 100644
--- a/drivers/net/netvsc/hn_rndis.c
+++ b/drivers/net/netvsc/hn_rndis.c
@@ -500,8 +500,10 @@ hn_rndis_query(struct hn_data *hv, uint32_t oid,
 	/* Input data immediately follows RNDIS query. */
 	memcpy(req + 1, idata, idlen);
 
+	rte_spinlock_lock(&hv->cmd_lock);
 	error = hn_rndis_execute(hv, rid, req, reqlen,
 				 comp, comp_len, RNDIS_QUERY_CMPLT);
+	rte_spinlock_unlock(&hv->cmd_lock);
 
 	if (error)
 		goto done;
diff --git a/drivers/net/netvsc/hn_var.h b/drivers/net/netvsc/hn_var.h
index 17c1d5d07b..66ed186c0a 100644
--- a/drivers/net/netvsc/hn_var.h
+++ b/drivers/net/netvsc/hn_var.h
@@ -179,6 +179,7 @@ struct hn_data {
 	struct vmbus_channel *channels[HN_MAX_CHANNELS];
 
 	rte_spinlock_t	hotadd_lock;
+	rte_spinlock_t	cmd_lock;
 	LIST_HEAD(hotadd_list, hv_hotadd_context) hotadd_list;
 };
 
-- 
2.50.1 (Apple Git-155)

RE: [EXTERNAL] [PATCH] net/netvsc: Fix on race condition of multiple commands

[Long Li]

> When multiple processes issue command requests(like: device info get and
> link-status) at same-time, then we could see the command request failures,
> due to race-condition of common function execution.

Hi Madhuker,

I'm not sure if we should use a lock in the driver for this. It's not clear in DPDK documents but in general the calls to query device status are not thread safe.

Is it possible that the application uses a lock to sync calling to this?

Thanks,
Long

> 
> So, to avoid such race-condition introduced a new spin-lock to protect the
> code of critical section.
> 
> Fixes: 4e9c73e96e83 ("net/netvsc: add Hyper-V network device")
> Signed-off-by: Madhuker Mythri <madhukar.mythri@gmail.com>
> ---
>  drivers/net/netvsc/hn_ethdev.c | 1 +
>  drivers/net/netvsc/hn_rndis.c  | 2 ++
>  drivers/net/netvsc/hn_var.h    | 1 +
>  3 files changed, 4 insertions(+)
> 
> diff --git a/drivers/net/netvsc/hn_ethdev.c b/drivers/net/netvsc/hn_ethdev.c
> index 6584819f4f..b525e287fa 100644
> --- a/drivers/net/netvsc/hn_ethdev.c
> +++ b/drivers/net/netvsc/hn_ethdev.c
> @@ -1310,6 +1310,7 @@ eth_hn_dev_init(struct rte_eth_dev *eth_dev)
>         PMD_INIT_FUNC_TRACE();
> 
>         rte_spinlock_init(&hv->hotadd_lock);
> +       rte_spinlock_init(&hv->cmd_lock);
>         LIST_INIT(&hv->hotadd_list);
> 
>         vmbus = container_of(device, struct rte_vmbus_device, device); diff --git
> a/drivers/net/netvsc/hn_rndis.c b/drivers/net/netvsc/hn_rndis.c index
> 7c54eebcef..8a0716df89 100644
> --- a/drivers/net/netvsc/hn_rndis.c
> +++ b/drivers/net/netvsc/hn_rndis.c
> @@ -500,8 +500,10 @@ hn_rndis_query(struct hn_data *hv, uint32_t oid,
>         /* Input data immediately follows RNDIS query. */
>         memcpy(req + 1, idata, idlen);
> 
> +       rte_spinlock_lock(&hv->cmd_lock);
>         error = hn_rndis_execute(hv, rid, req, reqlen,
>                                  comp, comp_len, RNDIS_QUERY_CMPLT);
> +       rte_spinlock_unlock(&hv->cmd_lock);
> 
>         if (error)
>                 goto done;
> diff --git a/drivers/net/netvsc/hn_var.h b/drivers/net/netvsc/hn_var.h index
> 17c1d5d07b..66ed186c0a 100644
> --- a/drivers/net/netvsc/hn_var.h
> +++ b/drivers/net/netvsc/hn_var.h
> @@ -179,6 +179,7 @@ struct hn_data {
>         struct vmbus_channel *channels[HN_MAX_CHANNELS];
> 
>         rte_spinlock_t  hotadd_lock;
> +       rte_spinlock_t  cmd_lock;
>         LIST_HEAD(hotadd_list, hv_hotadd_context) hotadd_list;  };
> 
> --
> 2.50.1 (Apple Git-155)

Re: [EXTERNAL] [PATCH] net/netvsc: Fix on race condition of multiple commands

[Stephen Hemminger]

On Fri, 19 Dec 2025 17:35:33 +0000
Long Li <longli@microsoft.com> wrote:

> > When multiple processes issue command requests(like: device info get and
> > link-status) at same-time, then we could see the command request failures,
> > due to race-condition of common function execution.  
> 
> Hi Madhuker,
> 
> I'm not sure if we should use a lock in the driver for this. It's not clear in DPDK documents but in general the calls to query device status are not thread safe.
> 
> Is it possible that the application uses a lock to sync calling to this?
> 

I do not know of any restrictions about threads calling query operations.

For info_get() the transaction is in rndis_get_offload().
There are couple of ways to handle this better. One would to do
the query during probe and remember the result. The hypervisor is
not going to change supported offload. The other and simpler way
would be to just have hardcoded offload values. The code for query
got compute offloads is inherited for BSD and unless someone was trying
to run on Windows 2012 or earlier version of Hyper-V it would never change.

Link status is a little more complex. Does the hyper-visor ever report
that the software path is down? And reading through the hn_rdis_exec code
it looks like if multiple operations are in process the second one
should return -EBUSY. Application could retry in that case.

Re: [EXTERNAL] [PATCH] net/netvsc: Fix on race condition of multiple commands

[madhukar mythri]

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Hi Li and Stephen,

We have a common DPDK application for all the PMD's, in which we are seeing
issue for this Netvsc PMD only.
I mean, for KVM hypervisor with Intel or Mellanox NICs we did not see such
sync issues. Also, with failsafe PMD on hyper-v did not seen such sync
issues.

So, i thought this would be better to fix at PMD level using spinlock.

@Stephen Hemminger <stephen@networkplumber.org> , yes we can store the
device info get details after probe and reuse it later.
For Link-status get with multiple threads we can go with retry mechanism.

However, w.r.t all other PMD's this device info get and Link-status get has
issues in multi threaded application.

Regards,
Madhuker.

On Sat, 20 Dec, 2025, 23:55 Stephen Hemminger, <stephen@networkplumber.org>
wrote:

> On Fri, 19 Dec 2025 17:35:33 +0000
> Long Li <longli@microsoft.com> wrote:
>
> > > When multiple processes issue command requests(like: device info get
> and
> > > link-status) at same-time, then we could see the command request
> failures,
> > > due to race-condition of common function execution.
> >
> > Hi Madhuker,
> >
> > I'm not sure if we should use a lock in the driver for this. It's not
> clear in DPDK documents but in general the calls to query device status are
> not thread safe.
> >
> > Is it possible that the application uses a lock to sync calling to this?
> >
>
> I do not know of any restrictions about threads calling query operations.
>
> For info_get() the transaction is in rndis_get_offload().
> There are couple of ways to handle this better. One would to do
> the query during probe and remember the result. The hypervisor is
> not going to change supported offload. The other and simpler way
> would be to just have hardcoded offload values. The code for query
> got compute offloads is inherited for BSD and unless someone was trying
> to run on Windows 2012 or earlier version of Hyper-V it would never change.
>
> Link status is a little more complex. Does the hyper-visor ever report
> that the software path is down? And reading through the hn_rdis_exec code
> it looks like if multiple operations are in process the second one
> should return -EBUSY. Application could retry in that case.
>

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