<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> <meta name="Generator" content="Microsoft Word 15 (filtered medium)"> <style></style> </head> <body lang="EN-US" link="blue" vlink="purple" style="word-wrap:break-word"> <div class="WordSection1"> <p class="MsoNormal">Hi Madhukar,<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">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?<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">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.<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Thanks,<o:p></o:p></p> <p class="MsoNormal">Long<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt"> <div> <div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in"> <p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> madhukar mythri <madhukar.mythri@gmail.com> <br> <b>Sent:</b> Saturday, December 20, 2025 9:37 PM<br> <b>To:</b> Stephen Hemminger <stephen@networkplumber.org><br> <b>Cc:</b> Long Li <longli@microsoft.com>; dev@dpdk.org; Madhuker Mythri <madhuker.mythri@oracle.com><br> <b>Subject:</b> Re: [EXTERNAL] [PATCH] net/netvsc: Fix on race condition of multiple commands<o:p></o:p></span></p> </div> </div> <p class="MsoNormal"><o:p> </o:p></p> <table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" align="left" width="100%" style="width:100.0%"> <tbody> <tr> <td width="0" style="width:.3pt;background:#A6A6A6;padding:5.25pt 1.5pt 5.25pt 1.5pt"> </td> <td width="100%" style="width:100.0%;background:#EAEAEA;padding:5.25pt 3.75pt 5.25pt 11.25pt;aspect-ratio: revert !important;background:revert !important;block-size: revert !important;border:revert !important;bottom: revert !important;color:revert !important;color-scheme: revert !important;content-visibility: revert !important;cursor:revert !important;direction:revert !important;display:revert !important;font-size:revert !important;height:revert !important;hyphens: revert !important;letter-spacing:revert !important;line-height:revert !important;margin:revert !important;opacity: revert !important;order: revert !important;outline: revert !important;overflow:revert !important;padding:revert !important;position:revert !important;resize: revert !important;rotate: revert !important;scale: revert !important;tab-size: revert !important;table-layout:revert !important;text-align:revert !important;text-indent:revert !important;text-orientation: revert !important;text-overflow: revert !important;text-shadow:revert !important;text-transform:revert !important;text-wrap: revert !important;top:revert !important;transition: revert !important;user-select: revert !important;vertical-align:revert !important;visibility:revert !important;white-space:revert !important;width:revert !important;word-break:revert !important;word-spacing:revert !important;writing-mode:revert !important;zoom: revert !important"> <div> <p class="MsoNormal" style="mso-element:frame;mso-element-frame-hspace:2.25pt;mso-element-wrap:around;mso-element-anchor-vertical:paragraph;mso-element-anchor-horizontal:column;mso-height-rule:exactly"> <span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif;color:#212121">You don't often get email from </span><span style="color:black"><a href="mailto:madhukar.mythri@gmail.com"><span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif">madhukar.mythri@gmail.com</span></a></span><span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif;color:#212121">. </span><span style="color:black"><a href="https://aka.ms/LearnAboutSenderIdentification"><span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif">Learn why this is important</span></a></span><span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif;color:#212121"> <o:p></o:p></span></p> </div> </td> <td width="75" style="width:56.25pt;background:#EAEAEA;padding:5.25pt 3.75pt 5.25pt 3.75pt;aspect-ratio: revert !important;background:revert !important;block-size: revert !important;border:revert !important;bottom: revert !important;color:revert !important;color-scheme: revert !important;content-visibility: revert !important;cursor:revert !important;direction:revert !important;display:revert !important;font-size:revert !important;height:revert !important;hyphens: revert !important;letter-spacing:revert !important;line-height:revert !important;margin:revert !important;opacity: revert !important;order: revert !important;outline: revert !important;overflow:revert !important;padding:revert !important;position:revert !important;resize: revert !important;rotate: revert !important;scale: revert !important;tab-size: revert !important;table-layout:revert !important;text-align:revert !important;text-indent:revert !important;text-orientation: revert !important;text-overflow: revert !important;text-shadow:revert !important;text-transform:revert !important;text-wrap: revert !important;top:revert !important;transition: revert !important;user-select: revert !important;vertical-align:revert !important;visibility:revert !important;white-space:revert !important;width:revert !important;word-break:revert !important;word-spacing:revert !important;writing-mode:revert !important;zoom: revert !important;align: left !important"> </td> </tr> </tbody> </table> <div> <div> <p class="MsoNormal">Hi Li and Stephen, <o:p></o:p></p> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">We have a common DPDK application for all the PMD's, in which we are seeing issue for this Netvsc PMD only.<o:p></o:p></p> </div> <div> <p class="MsoNormal">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.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">So, i thought this would be better to fix at PMD level using spinlock.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal"><a href="mailto:stephen@networkplumber.org"><span style="color:#1155CC">@Stephen Hemminger</span></a> , yes we can store the device info get details after probe and reuse it later.<o:p></o:p></p> </div> <div> <p class="MsoNormal">For Link-status get with multiple threads we can go with retry mechanism.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">However, w.r.t all other PMD's this device info get and Link-status get has issues in multi threaded application.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">Regards,<o:p></o:p></p> </div> <div> <p class="MsoNormal">Madhuker.<o:p></o:p></p> </div> </div> <p class="MsoNormal"><o:p> </o:p></p> <div> <div> <p class="MsoNormal">On Sat, 20 Dec, 2025, 23:55 Stephen Hemminger, <<a href="mailto:stephen@networkplumber.org">stephen@networkplumber.org</a>> wrote:<o:p></o:p></p> </div> <blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt"> <p class="MsoNormal">On Fri, 19 Dec 2025 17:35:33 +0000<br> Long Li <<a href="mailto:longli@microsoft.com" target="_blank">longli@microsoft.com</a>> wrote:<br> <br> > > When multiple processes issue command requests(like: device info get and<br> > > link-status) at same-time, then we could see the command request failures,<br> > > due to race-condition of common function execution. <br> > <br> > Hi Madhuker,<br> > <br> > 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.<br> > <br> > Is it possible that the application uses a lock to sync calling to this?<br> > <br> <br> I do not know of any restrictions about threads calling query operations.<br> <br> For info_get() the transaction is in rndis_get_offload().<br> There are couple of ways to handle this better. One would to do<br> the query during probe and remember the result. The hypervisor is<br> not going to change supported offload. The other and simpler way<br> would be to just have hardcoded offload values. The code for query<br> got compute offloads is inherited for BSD and unless someone was trying<br> to run on Windows 2012 or earlier version of Hyper-V it would never change.<br> <br> Link status is a little more complex. Does the hyper-visor ever report<br> that the software path is down? And reading through the hn_rdis_exec code<br> it looks like if multiple operations are in process the second one<br> should return -EBUSY. Application could retry in that case.<o:p></o:p></p> </blockquote> </div> </div> </div> </div> </body> </html>