Re: [Bug 214523] New: RDMA Mellanox RoCE drivers are unresponsive to ARP updates during a reconnect

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Sep 27, 2021 at 08:55:19PM +0800, Mark Zhang wrote:
> On 9/27/2021 8:24 PM, Jason Gunthorpe wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > On Mon, Sep 27, 2021 at 03:09:44PM +0300, Leon Romanovsky wrote:
> > > On Sun, Sep 26, 2021 at 05:36:01PM +0000, Chuck Lever III wrote:
> > > > Hi Leon-
> > > > 
> > > > Thanks for the suggestion! More below.
> > > > 
> > > > > On Sep 26, 2021, at 4:02 AM, Leon Romanovsky <leon@kernel.org> wrote:
> > > > > 
> > > > > On Fri, Sep 24, 2021 at 03:34:32PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:
> > > > > > https://bugzilla.kernel.org/show_bug.cgi?id=214523
> > > > > > 
> > > > > >             Bug ID: 214523
> > > > > >            Summary: RDMA Mellanox RoCE drivers are unresponsive to ARP
> > > > > >                     updates during a reconnect
> > > > > >            Product: Drivers
> > > > > >            Version: 2.5
> > > > > >     Kernel Version: 5.14
> > > > > >           Hardware: All
> > > > > >                 OS: Linux
> > > > > >               Tree: Mainline
> > > > > >             Status: NEW
> > > > > >           Severity: normal
> > > > > >           Priority: P1
> > > > > >          Component: Infiniband/RDMA
> > > > > >           Assignee: drivers_infiniband-rdma@kernel-bugs.osdl.org
> > > > > >           Reporter: kolga@netapp.com
> > > > > >         Regression: No
> > > > > > 
> > > > > > RoCE RDMA connection uses CMA protocol to establish an RDMA connection. During
> > > > > > the setup the code uses hard coded timeout/retry values. These values are used
> > > > > > for when Connect Request is not being answered to to re-try the request. During
> > > > > > the re-try attempts the ARP updates of the destination server are ignored.
> > > > > > Current timeout values lead to 4+minutes long attempt at connecting to a server
> > > > > > that no longer owns the IP since the ARP update happens.
> > > > > > 
> > > > > > The ask is to make the timeout/retry values configurable via procfs or sysfs.
> > > > > > This will allow for environments that use RoCE to reduce the timeouts to a more
> > > > > > reasonable values and be able to react to the ARP updates faster. Other CMA
> > > > > > users (eg IB or others) can continue to use existing values.
> > > > 
> > > > I would rather not add a user-facing tunable. The fabric should
> > > > be better at detecting addressing changes within a reasonable
> > > > time. It would be helpful to provide a history of why the ARP
> > > > timeout is so lax -- do certain ULPs rely on it being long?
> > > 
> > > I don't know about ULPs and ARPs, but how to calculate TimeWait is
> > > described in the spec.
> > > 
> > > Regarding tunable, I agree. Because it needs to be per-connection, most
> > > likely not many people in the world will success to configure it properly.
> > 
> > Maybe we should be disconnecting the cm_id if a gratituous ARP changes
> > the MAC address? The cm_id is surely broken after that event right?
> 
> Is there an event on gratuitous ARP? And we also need to notify user-space
> application, right?

I think there is a net notifier for this?

Userspace will see it via the CM event we'll need to trigger.

Jason