SUNRPC: Server-side disconnect injection

Disconnect injection stress-tests the ability for both client and
server implementations to behave resiliently in the face of network
instability.

A file called /sys/kernel/debug/fail_sunrpc/ignore-server-disconnect
enables administrators to turn off server-side disconnect injection
while allowing other types of sunrpc errors to be injected. So far
there are no others. The default setting is that server-side
disconnect injection is enabled (ignore=false).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/debugfs.c

@@ -308,8 +308,13 @@ struct fail_sunrpc_attr fail_sunrpc = {
 #if IS_ENABLED(CONFIG_FAULT_INJECTION_DEBUG_FS)
 static void fail_sunrpc_init(void)
 {
-	fault_create_debugfs_attr("fail_sunrpc", NULL,
-				  &fail_sunrpc.attr);
+	struct dentry *dir;
+
+	dir = fault_create_debugfs_attr("fail_sunrpc", NULL,
+					&fail_sunrpc.attr);
+
+	debugfs_create_bool("ignore-server-disconnect", S_IFREG | 0600, dir,
+			    &fail_sunrpc.ignore_server_disconnect);
 }
 #else
 static inline void fail_sunrpc_init(void)

net/sunrpc/fail.h

@@ -12,6 +12,8 @@
 
 struct fail_sunrpc_attr {
 	struct fault_attr	attr;
+
+	bool			ignore_server_disconnect;
 };
 
 extern struct fail_sunrpc_attr fail_sunrpc;

net/sunrpc/svc.c

@@ -31,6 +31,8 @@
 
 #include <trace/events/sunrpc.h>
 
+#include "fail.h"
+
 #define RPCDBG_FACILITY	RPCDBG_SVCDSP
 
 static void svc_unregister(const struct svc_serv *serv, struct net *net);
@@ -1503,6 +1505,12 @@ svc_process(struct svc_rqst *rqstp)
 	struct svc_serv		*serv = rqstp->rq_server;
 	u32			dir;
 
+#if IS_ENABLED(CONFIG_FAULT_INJECTION)
+	if (!fail_sunrpc.ignore_server_disconnect &&
+	    should_fail(&fail_sunrpc.attr, 1))
+		svc_xprt_deferred_close(rqstp->rq_xprt);
+#endif
+
 	/*
 	 * Setup response xdr_buf.
 	 * Initially it has just one page