Hi Madhukar, I suggest caching the result of hn_rndis_query_hwcaps(), as suggested by Stephen. This can be done inside PMD. Do you want me to submit a patch?
For querying link status, the lock should be implemented inside hn_rndis_exec1(). The drawback is that this function can potentially wait for up to 60 seconds on response from host, maybe not suitable for spinlock in production use. But I think it's better to have application retry on BUSY (with some delay logic), as the netvsc is designed in this way since introduced. Thanks, Long From: madhukar mythri <[email protected]> Sent: Saturday, December 20, 2025 9:37 PM To: Stephen Hemminger <[email protected]> Cc: Long Li <[email protected]>; [email protected]; Madhuker Mythri <[email protected]> Subject: Re: [EXTERNAL] [PATCH] net/netvsc: Fix on race condition of multiple commands You don't often get email from [email protected]<mailto:[email protected]>. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification> 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<mailto:[email protected]> , 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, <[email protected]<mailto:[email protected]>> wrote: On Fri, 19 Dec 2025 17:35:33 +0000 Long Li <[email protected]<mailto:[email protected]>> 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.
