SUNRPC: avoid soft lockup when transmitting UDP to reachable server.

Commit Message

NeilBrown June 19, 2024, 1:05 a.m. UTC

Prior to the commit identified below, call_transmit_status() would
handle -EPERM and other errors related to an unreachable server by
falling through to call_status() which added a 3-second delay and
handled the failure as a timeout.

Since that commit, call_transmit_status() falls through to
handle_bind().  For UDP this moves straight on to handle_connect() and
handle_transmit() so we immediately retransmit - and likely get the same
error.

This results in an indefinite loop in __rpc_execute() which triggers a
soft-lockup warning.

For the errors that indicate an unreachable server,
call_transmit_status() should fall back to call_status() as it did
before.  This cannot cause the thundering herd that the previous patch
was avoiding, as the call_status() will insert a delay.

Fixes: ed7dc973bd91 ("SUNRPC: Prevent thundering herd when the socket is not connected")
Signed-off-by: NeilBrown <[e-mail]>
---
 net/sunrpc/clnt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Patch

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index cfd1b1bf7e35..09f29a95f2bc 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2326,12 +2326,13 @@  call_transmit_status(struct rpc_task *task)
 		task->tk_action = call_transmit;
 		task->tk_status = 0;
 		break;
-	case -ECONNREFUSED:
 	case -EHOSTDOWN:
 	case -ENETDOWN:
 	case -EHOSTUNREACH:
 	case -ENETUNREACH:
 	case -EPERM:
+		break;
+	case -ECONNREFUSED:
 		if (RPC_IS_SOFTCONN(task)) {
 			if (!task->tk_msg.rpc_proc->p_proc)
 				trace_xprt_ping(task->tk_xprt,