Re: [Devel] [PATCH VZ10] fs/fuse kio: fix RPC response drop for large messages sent over RDMA

[Konstantin Khorenko <khorenko@virtuozzo.com>]

Liu, also please let me know if this patch replacement (ok, replacement with some next fixed version you send soon)
is a must for HCI 8 release or we can release the HCI 8 kernel as is and change the patch later in next releases.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 9/14/26 12:40, Liu Kui wrote:
> When a large message is sent via RDMA READ, it is completed with
> rio_msg_sent() - which moves the request onto the RPC pending queue
> where the response lookup can find it - only after both the
> RDMA_READ_REQ TX completion and the peer's RDMA_READ_ACK have been
> observed. However these two events are independent and not ordered:
> the ACK, and even the response to the request, can arrive before the
> local TX completion is polled. When that happens, the response finds
> no matching request on the RPC pending queue and is dropped, stalling
> the request until the RPC timeout logic kicks in.
> 
> Fix it by completing the message in rio_handle_rx_read_ack() as soon
> as the RDMA_READ_ACK arrives. Messages in a single RX queue are
> guaranteed to be delivered in order, so the ACK is always processed
> before the response, and the request is therefore on the RPC pending
> queue by the time its response arrives. This is also what the comment
> in rio_submit() has promised all along.
> 
> The tx buffer is still recycled only after both events have been seen.
> A TX send failure is handled by the connection abort logic as before.
> The same applies to an error status carried in the RDMA_READ_ACK:
> since the request msg has already been added to the rpc's pending
> queue, the rio abort triggers an rpc abort, which completes the msg
> with the same PCS_ERR_NET_ABORT error as before.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-141673
> 
> Signed-off-by: Liu Kui <kui.liu@virtuozzo.com>
> ---
>  fs/fuse/kio/pcs/pcs_rdma_io.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/fs/fuse/kio/pcs/pcs_rdma_io.c b/fs/fuse/kio/pcs/pcs_rdma_io.c
> index 1c464e0e60f3..14beab8fda8c 100644
> --- a/fs/fuse/kio/pcs/pcs_rdma_io.c
> +++ b/fs/fuse/kio/pcs/pcs_rdma_io.c
> @@ -797,7 +797,6 @@ static inline void rio_kick_write_queue(struct pcs_rdmaio *rio)
>  
>  static void rio_handle_tx(struct pcs_rdmaio *rio, struct rio_tx *tx, int ok)
>  {
> -	struct pcs_msg *msg = tx->msg;
>  	u64 xid = tx->xid;
>  
>  	/* override remote success if we already aborted */
> @@ -825,13 +824,6 @@ static void rio_handle_tx(struct pcs_rdmaio *rio, struct rio_tx *tx, int ok)
>  		default:
>  			BUG();
>  	}
> -
> -	if (msg) {
> -		if (!ok)
> -			pcs_set_local_error(&msg->error, PCS_ERR_NET_ABORT);
> -
> -		rio_msg_sent(rio, NULL, msg, 1);
> -	}
>  }
>  
>  /*
> @@ -931,6 +923,7 @@ static int rio_handle_rx_read_ack(struct pcs_rdmaio *rio,
>  
>  	list_for_each_entry(tx, &rio->active_txs, list)
>  		if (tx->xid == rack->xid) {
> +			rio_msg_sent(rio, NULL, tx->msg, 1);
>  			list_del(&tx->list);
>  			rio_handle_tx(rio, tx, !rack->status);
>  			return 0;

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