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

[Leon Romanovsky <leon@kernel.org>]

On Tue, Sep 08, 2026 at 08:44:25AM -0700, Ammar Ratnani wrote:
> 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
> 
> There, you can find: logs from the "bad" and "good" kernels, the kernel
> configuration, the VMs' configuration, and a playbook to trigger the hang.
> 
> Ammar Ratnani (2):
>   infiniband: force disconnect if DREP and DREQ fail
>   infiniband: trace force disconnections

I squashed the second patch into the first one, fixed the subject, removed
the useless AI-generated comments, placed trace call into right place, and
pushed the result.

Thanks

> 
>  drivers/infiniband/core/cma.c       | 41 ++++++++++++++++++++++++++---
>  drivers/infiniband/core/cma_trace.h |  1 +
>  2 files changed, 38 insertions(+), 4 deletions(-)
> 
> -- 
> 2.55.0