Re: [PATCH 0/2] smbdirect: don't hang on netdev reconfiguration

[Stefan Metzmacher <metze@samba.org>]

Hi Ammar,

thanks for the fixes!
I let the rdma maintainers comment on the patches in detail,
but it's good to fix these problems where they happen.

> When I mount a CIFS share using SMB Direct over RoCEv2, I observe a kernel
> thread hang if I "configure" its slave network device by taking its link
> down and bringing it back up. Attempting to just `ls` the mount point in
> this state gives EHOSTDOWN.
> 
> I believe the following is the root-cause of the hang: When the link is
> taken down, the corresponding GID Table Entry is marked as pending deletion
> and has its slave ndev set to NULL. All sends on RDMA connections still
> using that GID Table Entry fail at MAD creation. SMB Direct eventually
> detects this and tries to disconnect / reconnect to recover. Unfortunately,
> disconnecting requires successfully sending either a DREQ or a DREP. Since
> neither of them even post, the connection remains in the RDMA_CM_CONNECT
> state, and no callback moves it out. The SMB Direct layer never gets the
> RDMA_CM_EVENT_DISCONNECTED it's waiting for, and hangs.
> 
> Fix this in the CMA. If we call `rdma_disconnect` on a connected connection
> and we fail to send both a DREP and a DREQ; disconnect, and thereby send
> the `RDMA_CM_EVENT_DISCONNECTED` event to SMB Direct.
> 
> I tested this change in QEMU using RXE. I ran Ubuntu 26.04.1 with a
> mainline kernel. On commit 9f0346dcbea3 ("Merge tag 'driver-core-7.3-rc2'
> of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core"),
> I reproduce the hang. With this patch applied, SMB Direct immediately
> disconnects and reconnects when the slave device is brought down then up.
> Listing and reading files from the mount point also work afterwards.
> 
> Artifacts for reproducing the hang and testing my fix are available at
> 
>      https://github.com/ammrat13/linux-cifs
Given you have some automation to reproduce it I'm
wondering if you could also test the iwarp case, see
https://lore.kernel.org/linux-rdma/20260805000159.321645-2-yunseong.kim@est.tech/

That was reported as fix for ksmbd, but I guess it
will also happen for the case your're seeing with rxe.
And your fixes are likely also good for ksmbd.

Thanks!
metze