diff --git a/nfs.conf b/nfs.conf
index 31994f61..8c714ff7 100644
--- a/nfs.conf
+++ b/nfs.conf
@@ -25,6 +25,8 @@
 # cred-cache-directory=
 # preferred-realm=
 # set-home=1
+# upcall-timeout=30
+# cancel-timed-out-upcalls=0
 #
 [lockd]
 # port=0
diff --git a/utils/gssd/gssd.c b/utils/gssd/gssd.c
index eb440470..4ca637f4 100644
--- a/utils/gssd/gssd.c
+++ b/utils/gssd/gssd.c
@@ -96,8 +96,29 @@ pthread_mutex_t clp_lock = PTHREAD_MUTEX_INITIALIZER;
 static bool signal_received = false;
 static struct event_base *evbase = NULL;
 
+int upcall_timeout = DEF_UPCALL_TIMEOUT;
+static bool cancel_timed_out_upcalls = false;
+
 TAILQ_HEAD(topdir_list_head, topdir) topdir_list;
 
+/*
+ * active_thread_list:
+ *
+ * 	used to track upcalls for timeout purposes.
+ *
+ * 	protected by the active_thread_list_lock mutex.
+ *
+ * 	upcall_thread_info structures are added to the tail of the list
+ * 	by start_upcall_thread(), so entries closer to the head of the list
+ * 	will be closer to hitting the upcall timeout.
+ *
+ * 	upcall_thread_info structures are removed from the list upon a
+ * 	sucessful join of the upcall thread by the watchdog thread (via
+ * 	scan_active_thread_list().
+ */
+TAILQ_HEAD(active_thread_list_head, upcall_thread_info) active_thread_list;
+pthread_mutex_t active_thread_list_lock = PTHREAD_MUTEX_INITIALIZER;
+
 struct topdir {
 	TAILQ_ENTRY(topdir) list;
 	TAILQ_HEAD(clnt_list_head, clnt_info) clnt_list;
@@ -436,6 +457,138 @@ gssd_clnt_krb5_cb(int UNUSED(fd), short UNUSED(which), void *data)
 	handle_krb5_upcall(clp);
 }
 
+/*
+ * scan_active_thread_list:
+ *
+ * Walks the active_thread_list, trying to join as many upcall threads as
+ * possible.  For threads that have terminated, the corresponding
+ * upcall_thread_info will be removed from the list and freed.  Threads that
+ * are still busy and have exceeded the upcall_timeout will cause an error to
+ * be logged and may be canceled (depending on the value of
+ * cancel_timed_out_upcalls).
+ *
+ * Returns the number of seconds that the watchdog thread should wait before
+ * calling scan_active_thread_list() again.
+ */
+static int
+scan_active_thread_list(void)
+{
+	struct upcall_thread_info *info;
+	struct timespec now;
+	unsigned int sleeptime;
+	bool sleeptime_set = false;
+	int err;
+	void *tret, *saveprev;
+
+	sleeptime = upcall_timeout;
+	pthread_mutex_lock(&active_thread_list_lock);
+	clock_gettime(CLOCK_MONOTONIC, &now);
+	TAILQ_FOREACH(info, &active_thread_list, list) {
+		err = pthread_tryjoin_np(info->tid, &tret);
+		switch (err) {
+		case 0:
+			/*
+			 * The upcall thread has either completed successfully, or
+			 * has been canceled _and_ has acted on the cancellation request
+			 * (i.e. has hit a cancellation point).  We can now remove the
+			 * upcall_thread_info from the list and free it.
+			 */
+			if (tret == PTHREAD_CANCELED)
+				printerr(3, "watchdog: thread id 0x%lx cancelled successfully\n",
+						info->tid);
+			saveprev = info->list.tqe_prev;
+			TAILQ_REMOVE(&active_thread_list, info, list);
+			free(info);
+			info = saveprev;
+			break;
+		case EBUSY:
+			/*
+			 * The upcall thread is still running.  If the timeout has expired
+			 * then we either cancel the thread, log an error, and do an error
+			 * downcall to the kernel (cancel_timed_out_upcalls=true) or simply
+			 * log an error (cancel_timed_out_upcalls=false).  In either case,
+			 * the error is logged only once.
+			 */
+			if (now.tv_sec >= info->timeout.tv_sec) {
+				if (cancel_timed_out_upcalls && !(info->flags & UPCALL_THREAD_CANCELED)) {
+					printerr(0, "watchdog: thread id 0x%lx timed out\n",
+							info->tid);
+					pthread_cancel(info->tid);
+					info->flags |= (UPCALL_THREAD_CANCELED|UPCALL_THREAD_WARNED);
+					do_error_downcall(info->fd, info->uid, -ETIMEDOUT);
+				} else {
+					if (!(info->flags & UPCALL_THREAD_WARNED)) {
+						printerr(0, "watchdog: thread id 0x%lx running for %ld seconds\n",
+								info->tid,
+								now.tv_sec - info->timeout.tv_sec + upcall_timeout);
+						info->flags |= UPCALL_THREAD_WARNED;
+					}
+				}
+			} else if (!sleeptime_set) {
+			/*
+			 * The upcall thread is still running, but the timeout has not yet
+			 * expired.  Calculate the time remaining until the timeout will
+			 * expire.  This is the amount of time the watchdog thread will
+			 * wait before running again.  We only need to do this for the busy
+			 * thread closest to the head of the list - entries appearing later
+			 * in the list will time out later.
+			 */
+				sleeptime = info->timeout.tv_sec - now.tv_sec;
+				sleeptime_set = true;
+			}
+			break;
+		default:
+			/* EDEADLK, EINVAL, and ESRCH... none of which should happen! */
+			printerr(0, "watchdog: attempt to join thread id 0x%lx returned %d (%s)!\n",
+					info->tid, err, strerror(err));
+			break;
+		}
+	}
+	pthread_mutex_unlock(&active_thread_list_lock);
+
+	return sleeptime;
+}
+
+static void *
+watchdog_thread_fn(void *UNUSED(arg))
+{
+	unsigned int sleeptime;
+
+	for (;;) {
+		sleeptime = scan_active_thread_list();
+		printerr(4, "watchdog: sleeping %u secs\n", sleeptime);
+		sleep(sleeptime);
+	}
+	return (void *)0;
+}
+
+static int
+start_watchdog_thread(void)
+{
+	pthread_attr_t attr;
+	pthread_t th;
+	int ret;
+
+	ret = pthread_attr_init(&attr);
+	if (ret != 0) {
+		printerr(0, "ERROR: failed to init pthread attr: ret %d: %s\n",
+			 ret, strerror(errno));
+		return ret;
+	}
+	ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+	if (ret != 0) {
+		printerr(0, "ERROR: failed to create pthread attr: ret %d: %s\n",
+			 ret, strerror(errno));
+		return ret;
+	}
+	ret = pthread_create(&th, &attr, watchdog_thread_fn, NULL);
+	if (ret != 0) {
+		printerr(0, "ERROR: pthread_create failed: ret %d: %s\n",
+			 ret, strerror(errno));
+	}
+	return ret;
+}
+
 static struct clnt_info *
 gssd_get_clnt(struct topdir *tdi, const char *name)
 {
@@ -825,7 +978,7 @@ sig_die(int signal)
 static void
 usage(char *progname)
 {
-	fprintf(stderr, "usage: %s [-f] [-l] [-M] [-n] [-v] [-r] [-p pipefsdir] [-k keytab] [-d ccachedir] [-t timeout] [-R preferred realm] [-D] [-H]\n",
+	fprintf(stderr, "usage: %s [-f] [-l] [-M] [-n] [-v] [-r] [-p pipefsdir] [-k keytab] [-d ccachedir] [-t timeout] [-R preferred realm] [-D] [-H] [-U upcall timeout] [-C]\n",
 		progname);
 	exit(1);
 }
@@ -846,6 +999,9 @@ read_gss_conf(void)
 #endif
 	context_timeout = conf_get_num("gssd", "context-timeout", context_timeout);
 	rpc_timeout = conf_get_num("gssd", "rpc-timeout", rpc_timeout);
+	upcall_timeout = conf_get_num("gssd", "upcall-timeout", upcall_timeout);
+	cancel_timed_out_upcalls = conf_get_bool("gssd", "cancel-timed-out-upcalls",
+						cancel_timed_out_upcalls);
 	s = conf_get_str("gssd", "pipefs-directory");
 	if (!s)
 		s = conf_get_str("general", "pipefs-directory");
@@ -887,7 +1043,7 @@ main(int argc, char *argv[])
 	verbosity = conf_get_num("gssd", "verbosity", verbosity);
 	rpc_verbosity = conf_get_num("gssd", "rpc-verbosity", rpc_verbosity);
 
-	while ((opt = getopt(argc, argv, "HDfvrlmnMp:k:d:t:T:R:")) != -1) {
+	while ((opt = getopt(argc, argv, "HDfvrlmnMp:k:d:t:T:R:U:C")) != -1) {
 		switch (opt) {
 			case 'f':
 				fg = 1;
@@ -938,6 +1094,12 @@ main(int argc, char *argv[])
 			case 'H':
 				set_home = false;
 				break;
+			case 'U':
+				upcall_timeout = atoi(optarg);
+				break;
+			case 'C':
+				cancel_timed_out_upcalls = true;
+				break;
 			default:
 				usage(argv[0]);
 				break;
@@ -1010,6 +1172,11 @@ main(int argc, char *argv[])
 	else
 		progname = argv[0];
 
+	if (upcall_timeout > MAX_UPCALL_TIMEOUT)
+		upcall_timeout = MAX_UPCALL_TIMEOUT;
+	else if (upcall_timeout < MIN_UPCALL_TIMEOUT)
+		upcall_timeout = MIN_UPCALL_TIMEOUT;
+
 	initerr(progname, verbosity, fg);
 #ifdef HAVE_LIBTIRPC_SET_DEBUG
 	/*
@@ -1068,6 +1235,14 @@ main(int argc, char *argv[])
 	}
 	event_add(inotify_ev, NULL);
 
+	TAILQ_INIT(&active_thread_list);
+
+	rc = start_watchdog_thread();
+	if (rc != 0) {
+		printerr(0, "ERROR: failed to start watchdog thread: %d\n", rc);
+		exit(EXIT_FAILURE);
+	}
+
 	TAILQ_INIT(&topdir_list);
 	gssd_scan();
 	daemon_ready();
diff --git a/utils/gssd/gssd.h b/utils/gssd/gssd.h
index 6d53647e..c52c5b48 100644
--- a/utils/gssd/gssd.h
+++ b/utils/gssd/gssd.h
@@ -50,6 +50,12 @@
 #define GSSD_DEFAULT_KEYTAB_FILE		"/etc/krb5.keytab"
 #define GSSD_SERVICE_NAME			"nfs"
 #define RPC_CHAN_BUF_SIZE			32768
+
+/* timeouts are in seconds */
+#define MIN_UPCALL_TIMEOUT			5
+#define DEF_UPCALL_TIMEOUT			30
+#define MAX_UPCALL_TIMEOUT			600
+
 /*
  * The gss mechanisms that we can handle
  */
@@ -91,10 +97,22 @@ struct clnt_upcall_info {
 	char			*service;
 };
 
+struct upcall_thread_info {
+	TAILQ_ENTRY(upcall_thread_info) list;
+	pthread_t		tid;
+	struct timespec		timeout;
+	uid_t			uid;
+	int			fd;
+	unsigned short		flags;
+#define UPCALL_THREAD_CANCELED	0x0001
+#define UPCALL_THREAD_WARNED	0x0002
+};
+
 void handle_krb5_upcall(struct clnt_info *clp);
 void handle_gssd_upcall(struct clnt_info *clp);
 void free_upcall_info(struct clnt_upcall_info *info);
 void gssd_free_client(struct clnt_info *clp);
+int do_error_downcall(int k5_fd, uid_t uid, int err);
 
 
 #endif /* _RPC_GSSD_H_ */
diff --git a/utils/gssd/gssd.man b/utils/gssd/gssd.man
index 9ae6def9..2a5384d3 100644
--- a/utils/gssd/gssd.man
+++ b/utils/gssd/gssd.man
@@ -8,7 +8,7 @@
 rpc.gssd \- RPCSEC_GSS daemon
 .SH SYNOPSIS
 .B rpc.gssd
-.RB [ \-DfMnlvrH ]
+.RB [ \-DfMnlvrHC ]
 .RB [ \-k
 .IR keytab ]
 .RB [ \-p
@@ -17,6 +17,10 @@ rpc.gssd \- RPCSEC_GSS daemon
 .IR ccachedir ]
 .RB [ \-t
 .IR timeout ]
+.RB [ \-T
+.IR timeout ]
+.RB [ \-U
+.IR timeout ]
 .RB [ \-R
 .IR realm ]
 .SH INTRODUCTION
@@ -275,7 +279,7 @@ seconds, which allows changing Kerberos tickets and identities frequently.
 The default is no explicit timeout, which means the kernel context will live
 the lifetime of the Kerberos service ticket used in its creation.
 .TP
-.B -T timeout
+.BI "-T " timeout
 Timeout, in seconds, to create an RPC connection with a server while
 establishing an authenticated gss context for a user.
 The default timeout is set to 5 seconds.
@@ -283,6 +287,18 @@ If you get messages like "WARNING: can't create tcp rpc_clnt to server
 %servername% for user with uid %uid%: RPC: Remote system error -
 Connection timed out", you should consider an increase of this timeout.
 .TP
+.BI "-U " timeout
+Timeout, in seconds, for upcall threads.  Threads executing longer than
+.I timeout
+seconds will cause an error message to be logged.  The default
+.I timeout
+is 30 seconds.  The minimum is 5 seconds.  The maximum is 600 seconds.
+.TP
+.B -C
+In addition to logging an error message for threads that have timed out,
+the thread will be canceled and an error of -ETIMEDOUT will be reported
+to the kernel.
+.TP
 .B -H
 Avoids setting $HOME to "/". This allows rpc.gssd to read per user k5identity
 files versus trying to read /.k5identity for each user.
@@ -350,6 +366,17 @@ Equivalent to
 Equivalent to
 .BR -R .
 .TP
+.B upcall-timeout
+Equivalent to
+.BR -U .
+.TP
+.B cancel-timed-out-upcalls
+Setting to
+.B true
+is equivalent to providing the
+.B -C
+flag.
+.TP
 .B set-home
 Setting to
 .B false
diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
index ebec414e..60f61836 100644
--- a/utils/gssd/gssd_proc.c
+++ b/utils/gssd/gssd_proc.c
@@ -81,11 +81,24 @@
 #include "gss_names.h"
 
 extern pthread_mutex_t clp_lock;
+extern pthread_mutex_t active_thread_list_lock;
+extern int upcall_timeout;
+extern TAILQ_HEAD(active_thread_list_head, upcall_thread_info) active_thread_list;
 
 /* Encryption types supported by the kernel rpcsec_gss code */
 int num_krb5_enctypes = 0;
 krb5_enctype *krb5_enctypes = NULL;
 
+/* Args for the cleanup_handler() */
+struct cleanup_args  {
+	OM_uint32 	*min_stat;
+	gss_buffer_t	acceptor;
+	gss_buffer_t	token;
+	struct authgss_private_data *pd;
+	AUTH		**auth;
+	CLIENT		**rpc_clnt;
+};
+
 /*
  * Parse the supported encryption type information
  */
@@ -184,7 +197,7 @@ out_err:
 	return;
 }
 
-static int
+int
 do_error_downcall(int k5_fd, uid_t uid, int err)
 {
 	char	buf[1024];
@@ -608,13 +621,50 @@ out:
 }
 
 /*
+ * cleanup_handler:
+ *
+ * Free any resources allocated by process_krb5_upcall().
+ *
+ * Runs upon normal termination of process_krb5_upcall as well as if the
+ * thread is canceled.
+ */
+static void
+cleanup_handler(void *arg)
+{
+	struct cleanup_args *args = (struct cleanup_args *)arg;
+
+	gss_release_buffer(args->min_stat, args->acceptor);
+	if (args->token->value)
+		free(args->token->value);
+#ifdef HAVE_AUTHGSS_FREE_PRIVATE_DATA
+	if (args->pd->pd_ctx_hndl.length != 0 || args->pd->pd_ctx != 0)
+		authgss_free_private_data(args->pd);
+#endif
+	if (*args->auth)
+		AUTH_DESTROY(*args->auth);
+	if (*args->rpc_clnt)
+		clnt_destroy(*args->rpc_clnt);
+}
+
+/*
+ * process_krb5_upcall:
+ *
  * this code uses the userland rpcsec gss library to create a krb5
  * context on behalf of the kernel
+ *
+ * This is the meat of the upcall thread.  Note that cancelability is disabled
+ * and enabled at various points to ensure that any resources reserved by the
+ * lower level libraries are released safely.
  */
 static void
-process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
-		    char *tgtname, char *service)
+process_krb5_upcall(struct clnt_upcall_info *info)
 {
+	struct clnt_info	*clp = info->clp;
+	uid_t			uid = info->uid;
+	int			fd = info->fd;
+	char			*srchost = info->srchost;
+	char			*tgtname = info->target;
+	char			*service = info->service;
 	CLIENT			*rpc_clnt = NULL;
 	AUTH			*auth = NULL;
 	struct authgss_private_data pd;
@@ -624,11 +674,13 @@ process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
 	gss_name_t		gacceptor = GSS_C_NO_NAME;
 	gss_OID			mech;
 	gss_buffer_desc		acceptor  = {0};
+	struct cleanup_args cleanup_args = {&min_stat, &acceptor, &token, &pd, &auth, &rpc_clnt};
 
 	token.length = 0;
 	token.value = NULL;
 	memset(&pd, 0, sizeof(struct authgss_private_data));
 
+	pthread_cleanup_push(cleanup_handler, &cleanup_args);
 	/*
 	 * If "service" is specified, then the kernel is indicating that
 	 * we must use machine credentials for this request.  (Regardless
@@ -650,6 +702,7 @@ process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
 	 * used for this case is not important.
 	 *
 	 */
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
 	if (uid != 0 || (uid == 0 && root_uses_machine_creds == 0 &&
 				service == NULL)) {
 
@@ -670,15 +723,21 @@ process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
 			goto out_return_error;
 		}
 	}
+	pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+	pthread_testcancel();
 
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
 	if (!authgss_get_private_data(auth, &pd)) {
 		printerr(1, "WARNING: Failed to obtain authentication "
 			    "data for user with uid %d for server %s\n",
 			 uid, clp->servername);
 		goto out_return_error;
 	}
+	pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+	pthread_testcancel();
 
 	/* Grab the context lifetime and acceptor name out of the ctx. */
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
 	maj_stat = gss_inquire_context(&min_stat, pd.pd_ctx, NULL, &gacceptor,
 				       &lifetime_rec, &mech, NULL, NULL, NULL);
 
@@ -690,37 +749,35 @@ process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
 		get_hostbased_client_buffer(gacceptor, mech, &acceptor);
 		gss_release_name(&min_stat, &gacceptor);
 	}
+	pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+	pthread_testcancel();
 
 	/*
 	 * The serialization can mean turning pd.pd_ctx into a lucid context. If
 	 * that happens then the pd.pd_ctx will be unusable, so we must never
 	 * try to use it after this point.
 	 */
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
 	if (serialize_context_for_kernel(&pd.pd_ctx, &token, &krb5oid, NULL)) {
 		printerr(1, "WARNING: Failed to serialize krb5 context for "
 			    "user with uid %d for server %s\n",
 			 uid, clp->servername);
 		goto out_return_error;
 	}
+	pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+	pthread_testcancel();
 
 	do_downcall(fd, uid, &pd, &token, lifetime_rec, &acceptor);
 
 out:
-	gss_release_buffer(&min_stat, &acceptor);
-	if (token.value)
-		free(token.value);
-#ifdef HAVE_AUTHGSS_FREE_PRIVATE_DATA
-	if (pd.pd_ctx_hndl.length != 0 || pd.pd_ctx != 0)
-		authgss_free_private_data(&pd);
-#endif
-	if (auth)
-		AUTH_DESTROY(auth);
-	if (rpc_clnt)
-		clnt_destroy(rpc_clnt);
+	pthread_cleanup_pop(1);
 
 	return;
 
 out_return_error:
+	pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+	pthread_testcancel();
+
 	do_error_downcall(fd, uid, downcall_err);
 	goto out;
 }
@@ -786,36 +843,69 @@ void free_upcall_info(struct clnt_upcall_info *info)
 }
 
 static void
-gssd_work_thread_fn(struct clnt_upcall_info *info)
+cleanup_clnt_upcall_info(void *arg)
 {
-	process_krb5_upcall(info->clp, info->uid, info->fd, info->srchost, info->target, info->service);
+	struct clnt_upcall_info *info = (struct clnt_upcall_info *)arg;
+
 	free_upcall_info(info);
 }
 
+static void
+gssd_work_thread_fn(struct clnt_upcall_info *info)
+{
+	pthread_cleanup_push(cleanup_clnt_upcall_info, info);
+	process_krb5_upcall(info);
+	pthread_cleanup_pop(1);
+}
+
+static struct upcall_thread_info *
+alloc_upcall_thread_info(void)
+{
+	struct upcall_thread_info *info;
+
+	info = malloc(sizeof(struct upcall_thread_info));
+	if (info == NULL)
+		return NULL;
+	memset(info, 0, sizeof(*info));
+	return info;
+}
+
 static int
-start_upcall_thread(void (*func)(struct clnt_upcall_info *), void *info)
+start_upcall_thread(void (*func)(struct clnt_upcall_info *), struct clnt_upcall_info *info)
 {
 	pthread_attr_t attr;
 	pthread_t th;
+	struct upcall_thread_info *tinfo;
 	int ret;
 
+	tinfo = alloc_upcall_thread_info();
+	if (!tinfo)
+		return -ENOMEM;
+	tinfo->fd = info->fd;
+	tinfo->uid = info->uid;
+
 	ret = pthread_attr_init(&attr);
 	if (ret != 0) {
 		printerr(0, "ERROR: failed to init pthread attr: ret %d: %s\n",
 			 ret, strerror(errno));
-		return ret;
-	}
-	ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
-	if (ret != 0) {
-		printerr(0, "ERROR: failed to create pthread attr: ret %d: "
-			 "%s\n", ret, strerror(errno));
+		free(tinfo);
 		return ret;
 	}
 
 	ret = pthread_create(&th, &attr, (void *)func, (void *)info);
-	if (ret != 0)
+	if (ret != 0) {
 		printerr(0, "ERROR: pthread_create failed: ret %d: %s\n",
 			 ret, strerror(errno));
+		free(tinfo);
+		return ret;
+	}
+	tinfo->tid = th;
+	pthread_mutex_lock(&active_thread_list_lock);
+	clock_gettime(CLOCK_MONOTONIC, &tinfo->timeout);
+	tinfo->timeout.tv_sec += upcall_timeout;
+	TAILQ_INSERT_TAIL(&active_thread_list, tinfo, list);
+	pthread_mutex_unlock(&active_thread_list_lock);
+
 	return ret;
 }
 
