[Devel] [PATCH RHEL9 COMMIT] fs/fuse kio: fix hang rpc over rdma io

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-427.44.1.vz9.80.x-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh9-5.14.0-427.44.1.vz9.80.33
------>
commit bac90074d56fb3242cfd4800dee7ac3d1192219a
Author: Liu Kui <kui.liu at virtuozzo.com>
Date:   Thu May 8 12:17:24 2025 +0800

    fs/fuse kio: fix hang rpc over rdma io
    
    When a large msg is being sent out over rdma and in the stage of waiting
    for read ack from peer, it is moved from rio->write_queue to rio->active_txs.
    
    However the msg in rio->active_txs is not checked by pcs_rdma_next_timeout()
    to return a correct timeout back to rpc, as a result the rpc timer is not
    started. When the peer somehow becomes unresponsive, the msg at rio->active_txs
    can be stuck at waiting for read ack stage forever, because it can't be killed
    by the calendar timer since it's now under network I/O. As a result, the rpc
    can hang forever without detecting the stuck msg at underlying rdma io.
    
    Apparently pcs_rdma_next_timeout should return the next timeout based on
    first msg in rio->active_txs.
    
    Fixes: 8a3ab7d6c2963 ("fs/fuse kio: implement support RDMA transport")
    https://virtuozzo.atlassian.net/browse/VSTOR-105982
    
    Signed-off-by: Liu Kui <kui.liu at virtuozzo.com>
    Acked-by: Alexey Kuznetsov <kuznet at virtuozzo.com>
    
    Feature: vStorage
---
 fs/fuse/kio/pcs/pcs_rdma_io.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_rdma_io.c b/fs/fuse/kio/pcs/pcs_rdma_io.c
index 1d9e648d2636e..1c464e0e60f3e 100644
--- a/fs/fuse/kio/pcs/pcs_rdma_io.c
+++ b/fs/fuse/kio/pcs/pcs_rdma_io.c
@@ -1683,14 +1683,21 @@ static unsigned long pcs_rdma_next_timeout(struct pcs_netio *netio)
 	struct pcs_rdmaio *rio = rio_from_netio(netio);
 	struct pcs_rpc *ep = netio->parent;
 	struct pcs_msg *msg;
+	struct rio_tx *tx;
 
 	BUG_ON(!mutex_is_locked(&ep->mutex));
 
-	if (list_empty(&rio->write_queue))
-		return 0;
+	if (!list_empty(&rio->active_txs)) {
+		tx = list_first_entry(&rio->active_txs, struct rio_tx, list);
+		return tx->msg->start_time + rio->send_timeout;
+	}
 
-	msg = list_first_entry(&rio->write_queue, struct pcs_msg, list);
-	return msg->start_time + rio->send_timeout;
+	if (!list_empty(&rio->write_queue)) {
+		msg = list_first_entry(&rio->write_queue, struct pcs_msg, list);
+		return msg->start_time + rio->send_timeout;
+	}
+
+	return 0;
 }
 
 static int pcs_rdma_sync_send(struct pcs_netio *netio, struct pcs_msg *msg)