nfsd: fix a NFSv4.1 Linux client mount stuck in CLOSE_WAIT

It was reported that a NFSv4.1 Linux client mount against
a FreeBSD12 server was hung, with the TCP connection in
CLOSE_WAIT state on the server.
When a NFSv4.1/4.2 mount is done and the back channel is
bound to the TCP connection, the soclose() is delayed until
a new TCP connection is bound to the back channel, due to
a reference count being held on the SVCXPRT structure in
the krpc for the socket. Without the soclose() call, the socket
will remain in CLOSE_WAIT and this somehow caused the Linux
client to hang.

This patch adds calls to soshutdown(.., SHUT_WR) that
are performed when the server side krpc sees that the
socket is no longer usable.  Since this can be done
before the back channel is bound to a new TCP connection,
it allows the TCP connection to proceed to CLOSED state.

PR:	254590
Reported by:	jbreitman@tildenparkcapital.com
Reviewed by:	tuexen
Comments by:	kevans
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D29526

1 files changed, 5 insertions, 0 deletions

diff --git a/sys/rpc/svc.c b/sys/rpc/svc.c
index a059096e7b77..be0f08ebca9d 100644
--- a/sys/rpc/svc.c
+++ b/sys/rpc/svc.c
@@ -203,6 +203,8 @@ svcpool_cleanup(SVCPOOL *pool)
 		mtx_unlock(&grp->sg_lock);
 	}
 	TAILQ_FOREACH_SAFE(xprt, &cleanup, xp_link, nxprt) {
+		if (xprt->xp_socket != NULL)
+			soshutdown(xprt->xp_socket, SHUT_WR);
 		SVC_RELEASE(xprt);
 	}
 
@@ -388,6 +390,8 @@ xprt_unregister(SVCXPRT *xprt)
 	xprt_unregister_locked(xprt);
 	mtx_unlock(&grp->sg_lock);
 
+	if (xprt->xp_socket != NULL)
+		soshutdown(xprt->xp_socket, SHUT_WR);
 	SVC_RELEASE(xprt);
 }
 
@@ -1078,6 +1082,7 @@ svc_checkidle(SVCGROUP *grp)
 
 	mtx_unlock(&grp->sg_lock);
 	TAILQ_FOREACH_SAFE(xprt, &cleanup, xp_link, nxprt) {
+		soshutdown(xprt->xp_socket, SHUT_WR);
 		SVC_RELEASE(xprt);
 	}
 	mtx_lock(&grp->sg_lock);