Re: [RFC PATCH] RDMA/iwcm: allow aborting an active connect awaiting CONNECT_REPLY

[Leon Romanovsky <leon@kernel.org>]

On Wed, Aug 05, 2026 at 02:02:00AM +0200, Yunseong Kim wrote:
> After a successful connect downcall, iw_cm_connect() returns with
> IWCM_F_CONNECT_WAIT still set and the cm_id in IW_CM_STATE_CONN_SENT.
> The only thing that clears the flag is the provider delivering
> IW_CM_EVENT_CONNECT_REPLY (cm_conn_rep_handler()).  Until that event
> arrives, iw_cm_disconnect() and destroy_cm_id() sleep uninterruptibly
> in
> 
> 	wait_event(cm_id_priv->connect_wait,
> 		   !test_bit(IWCM_F_CONNECT_WAIT, &cm_id_priv->flags));
> 
> and both state machines treat IW_CM_STATE_CONN_SENT as BUG(), so the
> API has no way to cancel a pending active connect.  If the provider
> never generates the reply, because the peer died in the middle of
> connection setup or because of a provider bug, every teardown path
> (rdma_disconnect(), rdma_destroy_id()) blocks in D state forever and
> the ULP cannot recover: there is no way to disconnect after
> rdma_connect() was called without risking an unbounded hang.
> 
> This class of problem is not theoretical.  The pending smbdirect
> change "smb: smbdirect: bound the disconnect wait in destroy_sync" [1]
> had to work around it on the ULP side:
> smbdirect_socket_destroy_sync() waited unbounded for the socket to
> reach SMBDIRECT_SOCKET_DISCONNECTED, a transition that depends on an
> asynchronous RDMA CM disconnect event, and when the peer died abruptly
> (a killed client, or Soft-RoCE/RXE where no graceful disconnect
> completes) that event never arrived.  The destroy ran on the single
> ksmbd-conn-release workqueue, every later connection release queued
> behind it in D state, and the whole server wedged until hung_task
> fired.  That change bounded the wait and drove the socket state
> machine to DISCONNECTED locally on timeout; ULPs should not have to
> resort to that, the CM should offer a teardown they can rely on.
> 
> IWCM_F_CONNECT_WAIT currently guards two different windows:
> 
>  * the connect/accept downcall into the provider being in progress;
>    teardown must keep waiting for that, it is short and bounded;
> 
>  * an issued active connect waiting for CONNECT_REPLY, which is
>    potentially unbounded.
> 
> Mark the second window with a new flag, IWCM_F_CONNECT_SENT: set by
> iw_cm_connect() once the downcall has returned successfully, cleared
> by cm_conn_rep_handler().  The teardown waits now complete when either
> the downcall has finished (!IWCM_F_CONNECT_WAIT, as before) or the
> pending-reply window has been entered (IWCM_F_CONNECT_SENT), and the
> previously BUG() CONN_SENT cases become:
> 
>  * iw_cm_disconnect(): return -ENOTCONN; there is no established
>    connection to disconnect, aborting is the destroy path's job;
> 
>  * destroy_cm_id(): abort the pending connect locally by moving to
>    DESTROYING and putting the QP into error so the provider tears the
>    connection attempt down.
> 
> A CONNECT_REPLY that arrives after the abort is dropped: either
> cm_work_handler() sees IWCM_F_DROP_EVENTS, or cm_conn_rep_handler()
> now recognizes IW_CM_STATE_DESTROYING (the abort and the reply
> serialize on cm_id_priv->lock) and frees the event without touching
> the QP that destroy_cm_id() already released.  The cm_id memory stays
> valid for such a late reply because the provider holds its own
> reference (cm_id->add_ref) for as long as it can deliver events.
> 
> The passive side has a sibling gap, where after a successful accept
> downcall the flag stays set until the provider's ESTABLISHED event
> arrives, which this patch deliberately does not change.
> 
> [1] https://github.com/smfrench/smb3-kernel/commit/26d0f82a02c8a9c9c8cdfc138acb7ed0bf8e01a9
> 
> Suggested-by: Stefan Metzmacher <metze@samba.org>
> Signed-off-by: Yunseong Kim <yunseong.kim@est.tech>
> ---
>  drivers/infiniband/core/iwcm.c | 76 +++++++++++++++++++++++++++++-----
>  drivers/infiniband/core/iwcm.h |  1 +
>  2 files changed, 67 insertions(+), 10 deletions(-)

I'm not sure what to do with this patch, as the iWARP folks have
remained silent.

Stefan,

Do you still need this patch? Have you tested it?

Thanks,