SUNRPC: Address RCU warning in net/sunrpc/svc.c

$ make C=1 W=1 net/sunrpc/svc.o
make[1]: Entering directory 'linux/obj/manet.1015granger.net'
  GEN     Makefile
  CALL    linux/server-development/scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  DESCEND bpf/resolve_btfids
  INSTALL libsubcmd_headers
  CC [M]  net/sunrpc/svc.o
  CHECK   linux/server-development/net/sunrpc/svc.c
linux/server-development/net/sunrpc/svc.c:1225:9: warning: incorrect type in argument 1 (different address spaces)
linux/server-development/net/sunrpc/svc.c:1225:9:    expected struct spinlock [usertype] *lock
linux/server-development/net/sunrpc/svc.c:1225:9:    got struct spinlock [noderef] __rcu *
linux/server-development/net/sunrpc/svc.c:1227:40: warning: incorrect type in argument 1 (different address spaces)
linux/server-development/net/sunrpc/svc.c:1227:40:    expected struct spinlock [usertype] *lock
linux/server-development/net/sunrpc/svc.c:1227:40:    got struct spinlock [noderef] __rcu *
make[1]: Leaving directory 'linux/obj/manet.1015granger.net'

Warning introduced by commit 913292c ("sched.h: Annotate
sighand_struct with __rcu").

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

Author: chucklever

net/sunrpc/svc.c

@@ -1164,6 +1164,7 @@ static void __svc_unregister(struct net *net, const u32 program, const u32 versi
  */
 static void svc_unregister(const struct svc_serv *serv, struct net *net)
 {
+	struct sighand_struct *sighand;
 	struct svc_program *progp;
 	unsigned long flags;
 	unsigned int i;
@@ -1180,9 +1181,12 @@ static void svc_unregister(const struct svc_serv *serv, struct net *net)
 		}
 	}
 
-	spin_lock_irqsave(&current->sighand->siglock, flags);
+	rcu_read_lock();
+	sighand = rcu_dereference(current->sighand);
+	spin_lock_irqsave(&sighand->siglock, flags);
 	recalc_sigpending();
-	spin_unlock_irqrestore(&current->sighand->siglock, flags);
+	spin_unlock_irqrestore(&sighand->siglock, flags);
+	rcu_read_unlock();
 }
 
 /*