ipmi: Rework locking and shutdown for hot remove

To handle hot remove of interfaces, a lot of rework had to be
done to the locking.  Several things were switched over to srcu
and shutdown for users and interfaces was added for cleaner
shutdown.
Signed-off-by: Corey Minyard <cminyard@mvista.com>

drivers/char/ipmi/ipmi_msghandler.c

@@ -197,8 +197,12 @@ MODULE_PARM_DESC(default_max_retries,
 struct ipmi_user {
 	struct list_head link;
 
-	/* Set to false when the user is destroyed. */
-	bool valid;
+	/*
+	 * Set to NULL when the user is destroyed, a pointer to myself
+	 * so srcu_dereference can be used on it.
+	 */
+	struct ipmi_user *self;
+	struct srcu_struct release_barrier;
 
 	struct kref refcount;
 
@@ -213,6 +217,23 @@ struct ipmi_user {
 	bool gets_events;
 };
 
+static struct ipmi_user *acquire_ipmi_user(struct ipmi_user *user, int *index)
+	__acquires(user->release_barrier)
+{
+	struct ipmi_user *ruser;
+
+	*index = srcu_read_lock(&user->release_barrier);
+	ruser = srcu_dereference(user->self, &user->release_barrier);
+	if (!ruser)
+		srcu_read_unlock(&user->release_barrier, *index);
+	return ruser;
+}
+
+static void release_ipmi_user(struct ipmi_user *user, int index)
+{
+	srcu_read_unlock(&user->release_barrier, index);
+}
+
 struct cmd_rcvr {
 	struct list_head link;
 
@@ -444,10 +465,11 @@ struct ipmi_smi {
 	struct list_head link;
 
 	/*
-	 * The list of upper layers that are using me.  seq_lock
-	 * protects this.
+	 * The list of upper layers that are using me.  seq_lock write
+	 * protects this.  Read protection is with srcu.
 	 */
 	struct list_head users;
+	struct srcu_struct users_srcu;
 
 	/* Used for wake ups at startup. */
 	wait_queue_head_t waitq;
@@ -467,12 +489,6 @@ struct ipmi_smi {
 	bool in_bmc_register;  /* Handle recursive situations.  Yuck. */
 	struct work_struct bmc_reg_work;
 
-	/*
-	 * This is the lower-layer's sender routine.  Note that you
-	 * must either be holding the ipmi_interfaces_mutex or be in
-	 * an umpreemptible region to use this.  You must fetch the
-	 * value into a local variable and make sure it is not NULL.
-	 */
 	const struct ipmi_smi_handlers *handlers;
 	void                     *send_info;
 
@@ -615,6 +631,7 @@ static DEFINE_MUTEX(ipmidriver_mutex);
 
 static LIST_HEAD(ipmi_interfaces);
 static DEFINE_MUTEX(ipmi_interfaces_mutex);
+DEFINE_STATIC_SRCU(ipmi_interfaces_srcu);
 
 /*
  * List of watchers that want to know when smi's are added and deleted.
@@ -722,51 +739,25 @@ struct watcher_entry {
 int ipmi_smi_watcher_register(struct ipmi_smi_watcher *watcher)
 {
 	struct ipmi_smi *intf;
-	LIST_HEAD(to_deliver);
-	struct watcher_entry *e, *e2;
+	int index;
 
 	mutex_lock(&smi_watchers_mutex);
 
-	mutex_lock(&ipmi_interfaces_mutex);
-
-	/* Build a list of things to deliver. */
-	list_for_each_entry(intf, &ipmi_interfaces, link) {
-		if (intf->intf_num == -1)
-			continue;
-		e = kmalloc(sizeof(*e), GFP_KERNEL);
-		if (!e)
-			goto out_err;
-		kref_get(&intf->refcount);
-		e->intf = intf;
-		e->intf_num = intf->intf_num;
-		list_add_tail(&e->link, &to_deliver);
-	}
-
-	/* We will succeed, so add it to the list. */
 	list_add(&watcher->link, &smi_watchers);
 
-	mutex_unlock(&ipmi_interfaces_mutex);
+	index = srcu_read_lock(&ipmi_interfaces_srcu);
+	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
+		int intf_num = READ_ONCE(intf->intf_num);
 
-	list_for_each_entry_safe(e, e2, &to_deliver, link) {
-		list_del(&e->link);
-		watcher->new_smi(e->intf_num, e->intf->si_dev);
-		kref_put(&e->intf->refcount, intf_free);
-		kfree(e);
+		if (intf_num == -1)
+			continue;
+		watcher->new_smi(intf_num, intf->si_dev);
 	}
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
 
 	mutex_unlock(&smi_watchers_mutex);
 
 	return 0;
-
- out_err:
-	mutex_unlock(&ipmi_interfaces_mutex);
-	mutex_unlock(&smi_watchers_mutex);
-	list_for_each_entry_safe(e, e2, &to_deliver, link) {
-		list_del(&e->link);
-		kref_put(&e->intf->refcount, intf_free);
-		kfree(e);
-	}
-	return -ENOMEM;
 }
 EXPORT_SYMBOL(ipmi_smi_watcher_register);
 
@@ -787,12 +778,14 @@ call_smi_watchers(int i, struct device *dev)
 {
 	struct ipmi_smi_watcher *w;
 
+	mutex_lock(&smi_watchers_mutex);
 	list_for_each_entry(w, &smi_watchers, link) {
 		if (try_module_get(w->owner)) {
 			w->new_smi(i, dev);
 			module_put(w->owner);
 		}
 	}
+	mutex_unlock(&smi_watchers_mutex);
 }
 
 static int
@@ -905,9 +898,17 @@ static int deliver_response(struct ipmi_smi *intf, struct ipmi_recv_msg *msg)
 		 * receive handler doesn't much meaning and has a deadlock
 		 * risk.  At this moment, simply skip it in that case.
 		 */
+		int index;
+		struct ipmi_user *user = acquire_ipmi_user(msg->user, &index);
 
-		struct ipmi_user *user = msg->user;
+		if (user) {
 			user->handler->ipmi_recv_hndl(msg, user->handler_data);
+			release_ipmi_user(msg->user, index);
+		} else {
+			/* User went away, give up. */
+			ipmi_free_recv_msg(msg);
+			rv = -EINVAL;
+		}
 	}
 
 	return rv;
@@ -1094,7 +1095,7 @@ int ipmi_create_user(unsigned int          if_num,
 {
 	unsigned long flags;
 	struct ipmi_user *new_user;
-	int           rv = 0;
+	int           rv = 0, index;
 	struct ipmi_smi *intf;
 
 	/*
@@ -1129,7 +1130,7 @@ int ipmi_create_user(unsigned int          if_num,
 	if (!new_user)
 		return -ENOMEM;
 
-	mutex_lock(&ipmi_interfaces_mutex);
+	index = srcu_read_lock(&ipmi_interfaces_srcu);
 	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
 		if (intf->intf_num == if_num)
 			goto found;
@@ -1139,6 +1140,10 @@ int ipmi_create_user(unsigned int          if_num,
 	goto out_kfree;
 
  found:
+	rv = init_srcu_struct(&new_user->release_barrier);
+	if (rv)
+		goto out_kfree;
+
 	/* Note that each existing user holds a refcount to the interface. */
 	kref_get(&intf->refcount);
 
@@ -1148,26 +1153,7 @@ int ipmi_create_user(unsigned int          if_num,
 	new_user->intf = intf;
 	new_user->gets_events = false;
 
-	if (!try_module_get(intf->handlers->owner)) {
-		rv = -ENODEV;
-		goto out_kref;
-	}
-
-	if (intf->handlers->inc_usecount) {
-		rv = intf->handlers->inc_usecount(intf->send_info);
-		if (rv) {
-			module_put(intf->handlers->owner);
-			goto out_kref;
-		}
-	}
-
-	/*
-	 * Hold the lock so intf->handlers is guaranteed to be good
-	 * until now
-	 */
-	mutex_unlock(&ipmi_interfaces_mutex);
-
-	new_user->valid = true;
+	rcu_assign_pointer(new_user->self, new_user);
 	spin_lock_irqsave(&intf->seq_lock, flags);
 	list_add_rcu(&new_user->link, &intf->users);
 	spin_unlock_irqrestore(&intf->seq_lock, flags);
@@ -1176,13 +1162,12 @@ int ipmi_create_user(unsigned int          if_num,
 		if (atomic_inc_return(&intf->event_waiters) == 1)
 			need_waiter(intf);
 	}
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
 	*user = new_user;
 	return 0;
 
-out_kref:
-	kref_put(&intf->refcount, intf_free);
 out_kfree:
-	mutex_unlock(&ipmi_interfaces_mutex);
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
 	kfree(new_user);
 	return rv;
 }
@@ -1190,26 +1175,25 @@ EXPORT_SYMBOL(ipmi_create_user);
 
 int ipmi_get_smi_info(int if_num, struct ipmi_smi_info *data)
 {
-	int           rv = 0;
+	int rv, index;
 	struct ipmi_smi *intf;
-	const struct ipmi_smi_handlers *handlers;
 
-	mutex_lock(&ipmi_interfaces_mutex);
+	index = srcu_read_lock(&ipmi_interfaces_srcu);
 	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
 		if (intf->intf_num == if_num)
 			goto found;
 	}
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
+
 	/* Not found, return an error */
-	rv = -EINVAL;
-	mutex_unlock(&ipmi_interfaces_mutex);
-	return rv;
+	return -EINVAL;
 
 found:
-	handlers = intf->handlers;
-	rv = -ENOSYS;
-	if (handlers->get_smi_info)
-		rv = handlers->get_smi_info(intf->send_info, data);
-	mutex_unlock(&ipmi_interfaces_mutex);
+	if (!intf->handlers->get_smi_info)
+		rv = -ENOTTY;
+	else
+		rv = intf->handlers->get_smi_info(intf->send_info, data);
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
 
 	return rv;
 }
@@ -1221,7 +1205,7 @@ static void free_user(struct kref *ref)
 	kfree(user);
 }
 
-int ipmi_destroy_user(struct ipmi_user *user)
+static void _ipmi_destroy_user(struct ipmi_user *user)
 {
 	struct ipmi_smi  *intf = user->intf;
 	int              i;
@@ -1229,7 +1213,22 @@ int ipmi_destroy_user(struct ipmi_user *user)
 	struct cmd_rcvr  *rcvr;
 	struct cmd_rcvr  *rcvrs = NULL;
 
-	user->valid = false;
+	if (!acquire_ipmi_user(user, &i)) {
+		/*
+		 * The user has already been cleaned up, just make sure
+		 * nothing is using it and return.
+		 */
+		synchronize_srcu(&user->release_barrier);
+		return;
+	}
+
+	rcu_assign_pointer(user->self, NULL);
+	release_ipmi_user(user, i);
+
+	synchronize_srcu(&user->release_barrier);
+
+	if (user->handler->shutdown)
+		user->handler->shutdown(user->handler_data);
 
 	if (user->handler->ipmi_watchdog_pretimeout)
 		atomic_dec(&intf->event_waiters);
@@ -1254,7 +1253,7 @@ int ipmi_destroy_user(struct ipmi_user *user)
 	 * Remove the user from the command receiver's table.  First
 	 * we build a list of everything (not using the standard link,
 	 * since other things may be using it till we do
-	 * synchronize_rcu()) then free everything in that list.
+	 * synchronize_srcu()) then free everything in that list.
 	 */
 	mutex_lock(&intf->cmd_rcvrs_mutex);
 	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
@@ -1272,16 +1271,14 @@ int ipmi_destroy_user(struct ipmi_user *user)
 		kfree(rcvr);
 	}
 
-	mutex_lock(&ipmi_interfaces_mutex);
-	if (intf->handlers) {
-		module_put(intf->handlers->owner);
-		if (intf->handlers->dec_usecount)
-			intf->handlers->dec_usecount(intf->send_info);
-	}
-	mutex_unlock(&ipmi_interfaces_mutex);
-
 	kref_put(&intf->refcount, intf_free);
+}
 
+int ipmi_destroy_user(struct ipmi_user *user)
+{
+	_ipmi_destroy_user(user);
+
+	cleanup_srcu_struct(&user->release_barrier);
 	kref_put(&user->refcount, free_user);
 
 	return 0;
@@ -1293,16 +1290,20 @@ int ipmi_get_version(struct ipmi_user *user,
 		     unsigned char *minor)
 {
 	struct ipmi_device_id id;
-	int rv;
+	int rv, index;
 
-	rv = bmc_get_device_id(user->intf, NULL, &id, NULL, NULL);
-	if (rv)
-		return rv;
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
 
+	rv = bmc_get_device_id(user->intf, NULL, &id, NULL, NULL);
+	if (!rv) {
 		*major = ipmi_version_major(&id);
 		*minor = ipmi_version_minor(&id);
+	}
+	release_ipmi_user(user, index);
 
-	return 0;
+	return rv;
 }
 EXPORT_SYMBOL(ipmi_get_version);
 
@@ -1310,9 +1311,17 @@ int ipmi_set_my_address(struct ipmi_user *user,
 			unsigned int  channel,
 			unsigned char address)
 {
+	int index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	if (channel >= IPMI_MAX_CHANNELS)
 		return -EINVAL;
 	user->intf->addrinfo[channel].address = address;
+	release_ipmi_user(user, index);
+
 	return 0;
 }
 EXPORT_SYMBOL(ipmi_set_my_address);
@@ -1321,9 +1330,17 @@ int ipmi_get_my_address(struct ipmi_user *user,
 			unsigned int  channel,
 			unsigned char *address)
 {
+	int index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	if (channel >= IPMI_MAX_CHANNELS)
 		return -EINVAL;
 	*address = user->intf->addrinfo[channel].address;
+	release_ipmi_user(user, index);
+
 	return 0;
 }
 EXPORT_SYMBOL(ipmi_get_my_address);
@@ -1332,9 +1349,17 @@ int ipmi_set_my_LUN(struct ipmi_user *user,
 		    unsigned int  channel,
 		    unsigned char LUN)
 {
+	int index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	if (channel >= IPMI_MAX_CHANNELS)
 		return -EINVAL;
 	user->intf->addrinfo[channel].lun = LUN & 0x3;
+	release_ipmi_user(user, index);
+
 	return 0;
 }
 EXPORT_SYMBOL(ipmi_set_my_LUN);
@@ -1343,21 +1368,34 @@ int ipmi_get_my_LUN(struct ipmi_user *user,
 		    unsigned int  channel,
 		    unsigned char *address)
 {
+	int index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	if (channel >= IPMI_MAX_CHANNELS)
 		return -EINVAL;
 	*address = user->intf->addrinfo[channel].lun;
+	release_ipmi_user(user, index);
+
 	return 0;
 }
 EXPORT_SYMBOL(ipmi_get_my_LUN);
 
 int ipmi_get_maintenance_mode(struct ipmi_user *user)
 {
-	int           mode;
+	int mode, index;
 	unsigned long flags;
 
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	spin_lock_irqsave(&user->intf->maintenance_mode_lock, flags);
 	mode = user->intf->maintenance_mode;
 	spin_unlock_irqrestore(&user->intf->maintenance_mode_lock, flags);
+	release_ipmi_user(user, index);
 
 	return mode;
 }
@@ -1372,10 +1410,14 @@ static void maintenance_mode_update(struct ipmi_smi *intf)
 
 int ipmi_set_maintenance_mode(struct ipmi_user *user, int mode)
 {
-	int           rv = 0;
+	int rv = 0, index;
 	unsigned long flags;
 	struct ipmi_smi *intf = user->intf;
 
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	spin_lock_irqsave(&intf->maintenance_mode_lock, flags);
 	if (intf->maintenance_mode != mode) {
 		switch (mode) {
@@ -1402,6 +1444,7 @@ int ipmi_set_maintenance_mode(struct ipmi_user *user, int mode)
 	}
  out_unlock:
 	spin_unlock_irqrestore(&intf->maintenance_mode_lock, flags);
+	release_ipmi_user(user, index);
 
 	return rv;
 }
@@ -1413,6 +1456,11 @@ int ipmi_set_gets_events(struct ipmi_user *user, bool val)
 	struct ipmi_smi      *intf = user->intf;
 	struct ipmi_recv_msg *msg, *msg2;
 	struct list_head     msgs;
+	int index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
 
 	INIT_LIST_HEAD(&msgs);
 
@@ -1462,6 +1510,7 @@ int ipmi_set_gets_events(struct ipmi_user *user, bool val)
 
  out:
 	spin_unlock_irqrestore(&intf->events_lock, flags);
+	release_ipmi_user(user, index);
 
 	return 0;
 }
@@ -1504,8 +1553,11 @@ int ipmi_register_for_cmd(struct ipmi_user *user,
 {
 	struct ipmi_smi *intf = user->intf;
 	struct cmd_rcvr *rcvr;
-	int             rv = 0;
+	int rv = 0, index;
 
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
 
 	rcvr = kmalloc(sizeof(*rcvr), GFP_KERNEL);
 	if (!rcvr)
@@ -1531,6 +1583,7 @@ int ipmi_register_for_cmd(struct ipmi_user *user,
 	mutex_unlock(&intf->cmd_rcvrs_mutex);
 	if (rv)
 		kfree(rcvr);
+	release_ipmi_user(user, index);
 
 	return rv;
 }
@@ -1544,7 +1597,11 @@ int ipmi_unregister_for_cmd(struct ipmi_user *user,
 	struct ipmi_smi *intf = user->intf;
 	struct cmd_rcvr *rcvr;
 	struct cmd_rcvr *rcvrs = NULL;
-	int i, rv = -ENOENT;
+	int i, rv = -ENOENT, index;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
 
 	mutex_lock(&intf->cmd_rcvrs_mutex);
 	for (i = 0; i < IPMI_NUM_CHANNELS; i++) {
@@ -1565,12 +1622,14 @@ int ipmi_unregister_for_cmd(struct ipmi_user *user,
 	}
 	mutex_unlock(&intf->cmd_rcvrs_mutex);
 	synchronize_rcu();
+	release_ipmi_user(user, index);
 	while (rcvrs) {
 		atomic_dec(&intf->event_waiters);
 		rcvr = rcvrs;
 		rcvrs = rcvr->next;
 		kfree(rcvr);
 	}
+
 	return rv;
 }
 EXPORT_SYMBOL(ipmi_unregister_for_cmd);
@@ -2065,8 +2124,10 @@ static int i_ipmi_request(struct ipmi_user     *user,
 		recv_msg = supplied_recv;
 	else {
 		recv_msg = ipmi_alloc_recv_msg();
-		if (recv_msg == NULL)
-			return -ENOMEM;
+		if (recv_msg == NULL) {
+			rv = -ENOMEM;
+			goto out;
+		}
 	}
 	recv_msg->user_msg_data = user_msg_data;
 
@@ -2076,7 +2137,8 @@ static int i_ipmi_request(struct ipmi_user     *user,
 		smi_msg = ipmi_alloc_smi_msg();
 		if (smi_msg == NULL) {
 			ipmi_free_recv_msg(recv_msg);
-			return -ENOMEM;
+			rv = -ENOMEM;
+			goto out;
 		}
 	}
 
@@ -2088,6 +2150,7 @@ static int i_ipmi_request(struct ipmi_user     *user,
 
 	recv_msg->user = user;
 	if (user)
+		/* The put happens when the message is freed. */
 		kref_get(&user->refcount);
 	recv_msg->msgid = msgid;
 	/*
@@ -2123,6 +2186,7 @@ static int i_ipmi_request(struct ipmi_user     *user,
 	}
 	rcu_read_unlock();
 
+out:
 	return rv;
 }
 
@@ -2148,14 +2212,18 @@ int ipmi_request_settime(struct ipmi_user *user,
 			 unsigned int     retry_time_ms)
 {
 	unsigned char saddr = 0, lun = 0;
-	int           rv;
+	int rv, index;
 
 	if (!user)
 		return -EINVAL;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	rv = check_addr(user->intf, addr, &saddr, &lun);
-	if (rv)
-		return rv;
-	return i_ipmi_request(user,
+	if (!rv)
+		rv = i_ipmi_request(user,
 				    user->intf,
 				    addr,
 				    msgid,
@@ -2167,6 +2235,9 @@ int ipmi_request_settime(struct ipmi_user *user,
 				    lun,
 				    retries,
 				    retry_time_ms);
+
+	release_ipmi_user(user, index);
+	return rv;
 }
 EXPORT_SYMBOL(ipmi_request_settime);
 
@@ -2180,14 +2251,18 @@ int ipmi_request_supply_msgs(struct ipmi_user     *user,
 			     int                  priority)
 {
 	unsigned char saddr = 0, lun = 0;
-	int           rv;
+	int rv, index;
 
 	if (!user)
 		return -EINVAL;
+
+	user = acquire_ipmi_user(user, &index);
+	if (!user)
+		return -ENODEV;
+
 	rv = check_addr(user->intf, addr, &saddr, &lun);
-	if (rv)
-		return rv;
-	return i_ipmi_request(user,
+	if (!rv)
+		rv = i_ipmi_request(user,
 				    user->intf,
 				    addr,
 				    msgid,
@@ -2199,6 +2274,9 @@ int ipmi_request_supply_msgs(struct ipmi_user     *user,
 				    saddr,
 				    lun,
 				    -1, 0);
+
+	release_ipmi_user(user, index);
+	return rv;
 }
 EXPORT_SYMBOL(ipmi_request_supply_msgs);
 
@@ -3455,6 +3533,13 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
 	if (!intf)
 		return -ENOMEM;
 
+	rv = init_srcu_struct(&intf->users_srcu);
+	if (rv) {
+		kfree(intf);
+		return rv;
+	}
+
+
 	intf->bmc = &intf->tmp_bmc;
 	INIT_LIST_HEAD(&intf->bmc->intfs);
 	mutex_init(&intf->bmc->dyn_mutex);
@@ -3507,7 +3592,6 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
 	intf->proc_dir = NULL;
 #endif
 
-	mutex_lock(&smi_watchers_mutex);
 	mutex_lock(&ipmi_interfaces_mutex);
 	/* Look for a hole in the numbers. */
 	i = 0;
@@ -3552,11 +3636,10 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
 		if (intf->proc_dir)
 			remove_proc_entries(intf);
 #endif
-		intf->handlers = NULL;
 		list_del_rcu(&intf->link);
 		mutex_unlock(&ipmi_interfaces_mutex);
-		mutex_unlock(&smi_watchers_mutex);
-		synchronize_rcu();
+		synchronize_srcu(&ipmi_interfaces_srcu);
+		cleanup_srcu_struct(&intf->users_srcu);
 		kref_put(&intf->refcount, intf_free);
 	} else {
 		/*
@@ -3567,9 +3650,9 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
 		smp_wmb();
 		intf->intf_num = i;
 		mutex_unlock(&ipmi_interfaces_mutex);
+
 		/* After this point the interface is legal to use. */
 		call_smi_watchers(i, intf->si_dev);
-		mutex_unlock(&smi_watchers_mutex);
 	}
 
 	return rv;
@@ -3631,45 +3714,49 @@ static void cleanup_smi_msgs(struct ipmi_smi *intf)
 int ipmi_unregister_smi(struct ipmi_smi *intf)
 {
 	struct ipmi_smi_watcher *w;
-	int intf_num = intf->intf_num;
-	struct ipmi_user *user;
+	int intf_num = intf->intf_num, index;
 
-	mutex_lock(&smi_watchers_mutex);
 	mutex_lock(&ipmi_interfaces_mutex);
 	intf->intf_num = -1;
 	intf->in_shutdown = true;
 	list_del_rcu(&intf->link);
 	mutex_unlock(&ipmi_interfaces_mutex);
-	synchronize_rcu();
+	synchronize_srcu(&ipmi_interfaces_srcu);
 
-	cleanup_smi_msgs(intf);
-
-	/* Clean up the effects of users on the lower-level software. */
-	mutex_lock(&ipmi_interfaces_mutex);
-	rcu_read_lock();
-	list_for_each_entry_rcu(user, &intf->users, link) {
-		module_put(intf->handlers->owner);
-		if (intf->handlers->dec_usecount)
-			intf->handlers->dec_usecount(intf->send_info);
-	}
-	rcu_read_unlock();
-	intf->handlers = NULL;
-	mutex_unlock(&ipmi_interfaces_mutex);
-
-#ifdef CONFIG_IPMI_PROC_INTERFACE
-	remove_proc_entries(intf);
-#endif
-	ipmi_bmc_unregister(intf);
+	/* At this point no users can be added to the interface. */
 
 	/*
 	 * Call all the watcher interfaces to tell them that
-	 * an interface is gone.
+	 * an interface is going away.
 	 */
+	mutex_lock(&smi_watchers_mutex);
 	list_for_each_entry(w, &smi_watchers, link)
 		w->smi_gone(intf_num);
 	mutex_unlock(&smi_watchers_mutex);
 
+	index = srcu_read_lock(&intf->users_srcu);
+	while (!list_empty(&intf->users)) {
+		struct ipmi_user *user =
+			container_of(list_next_rcu(&intf->users),
+				     struct ipmi_user, link);
+
+		_ipmi_destroy_user(user);
+	}
+	srcu_read_unlock(&intf->users_srcu, index);
+
+	if (intf->handlers->shutdown)
+		intf->handlers->shutdown(intf->send_info);
+
+	cleanup_smi_msgs(intf);
+
+#ifdef CONFIG_IPMI_PROC_INTERFACE
+	remove_proc_entries(intf);
+#endif
+	ipmi_bmc_unregister(intf);
+
+	cleanup_srcu_struct(&intf->users_srcu);
 	kref_put(&intf->refcount, intf_free);
+
 	return 0;
 }
 EXPORT_SYMBOL(ipmi_unregister_smi);
@@ -4141,8 +4228,7 @@ static int handle_read_event_rsp(struct ipmi_smi *intf,
 	struct ipmi_recv_msg *recv_msg, *recv_msg2;
 	struct list_head     msgs;
 	struct ipmi_user     *user;
-	int                  rv = 0;
-	int                  deliver_count = 0;
+	int rv = 0, deliver_count = 0, index;
 	unsigned long        flags;
 
 	if (msg->rsp_size < 19) {
@@ -4166,7 +4252,7 @@ static int handle_read_event_rsp(struct ipmi_smi *intf,
 	 * Allocate and fill in one message for every user that is
 	 * getting events.
 	 */
-	rcu_read_lock();
+	index = srcu_read_lock(&intf->users_srcu);
 	list_for_each_entry_rcu(user, &intf->users, link) {
 		if (!user->gets_events)
 			continue;
@@ -4195,7 +4281,7 @@ static int handle_read_event_rsp(struct ipmi_smi *intf,
 		kref_get(&user->refcount);
 		list_add_tail(&recv_msg->link, &msgs);
 	}
-	rcu_read_unlock();
+	srcu_read_unlock(&intf->users_srcu, index);
 
 	if (deliver_count) {
 		/* Now deliver all the messages. */
@@ -4242,7 +4328,7 @@ static int handle_bmc_rsp(struct ipmi_smi *intf,
 			  struct ipmi_smi_msg *msg)
 {
 	struct ipmi_recv_msg *recv_msg;
-	struct ipmi_user     *user;
+	struct ipmi_system_interface_addr *smi_addr;
 
 	recv_msg = (struct ipmi_recv_msg *) msg->user_data;
 	if (recv_msg == NULL) {
@@ -4251,16 +4337,6 @@ static int handle_bmc_rsp(struct ipmi_smi *intf,
 		return 0;
 	}
 
-	user = recv_msg->user;
-	/* Make sure the user still exists. */
-	if (user && !user->valid) {
-		/* The user for the message went away, so give up. */
-		ipmi_inc_stat(intf, unhandled_local_responses);
-		ipmi_free_recv_msg(recv_msg);
-	} else {
-		struct ipmi_system_interface_addr *smi_addr;
-
-		ipmi_inc_stat(intf, handled_local_responses);
 	recv_msg->recv_type = IPMI_RESPONSE_RECV_TYPE;
 	recv_msg->msgid = msg->msgid;
 	smi_addr = ((struct ipmi_system_interface_addr *)
@@ -4274,7 +4350,6 @@ static int handle_bmc_rsp(struct ipmi_smi *intf,
 	recv_msg->msg.data = recv_msg->msg_data;
 	recv_msg->msg.data_len = msg->rsp_size - 2;
 	deliver_local_response(intf, recv_msg);
-	}
 
 	return 0;
 }
@@ -4342,10 +4417,6 @@ static int handle_one_recv_msg(struct ipmi_smi *intf,
 		if (!recv_msg)
 			goto out;
 
-		/* Make sure the user still exists. */
-		if (!recv_msg->user || !recv_msg->user->valid)
-			goto out;
-
 		recv_msg->recv_type = IPMI_RESPONSE_RESPONSE_TYPE;
 		recv_msg->msg.data = recv_msg->msg_data;
 		recv_msg->msg.data_len = 1;
@@ -4488,14 +4559,15 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf)
 	 */
 	if (atomic_add_unless(&intf->watchdog_pretimeouts_to_deliver, -1, 0)) {
 		struct ipmi_user *user;
+		int index;
 
-		rcu_read_lock();
+		index = srcu_read_lock(&intf->users_srcu);
 		list_for_each_entry_rcu(user, &intf->users, link) {
 			if (user->handler->ipmi_watchdog_pretimeout)
 				user->handler->ipmi_watchdog_pretimeout(
 					user->handler_data);
 		}
-		rcu_read_unlock();
+		srcu_read_unlock(&intf->users_srcu, index);
 	}
 }
 
@@ -4663,7 +4735,6 @@ static void check_msg_timeout(struct ipmi_smi *intf, struct seq_table *ent,
 			      unsigned int *waiting_msgs)
 {
 	struct ipmi_recv_msg *msg;
-	const struct ipmi_smi_handlers *handlers;
 
 	if (intf->in_shutdown)
 		return;
@@ -4721,8 +4792,7 @@ static void check_msg_timeout(struct ipmi_smi *intf, struct seq_table *ent,
 		 * only for messages to the local MC, which don't get
 		 * resent.
 		 */
-		handlers = intf->handlers;
-		if (handlers) {
+		if (intf->handlers) {
 			if (is_lan_addr(&ent->recv_msg->addr))
 				ipmi_inc_stat(intf,
 					      retransmitted_lan_commands);
@@ -4730,7 +4800,7 @@ static void check_msg_timeout(struct ipmi_smi *intf, struct seq_table *ent,
 				ipmi_inc_stat(intf,
 					      retransmitted_ipmb_commands);
 
-			smi_send(intf, handlers, smi_msg, 0);
+			smi_send(intf, intf->handlers, smi_msg, 0);
 		} else
 			ipmi_free_smi_msg(smi_msg);
 
@@ -4822,12 +4892,12 @@ static atomic_t stop_operation;
 static void ipmi_timeout(struct timer_list *unused)
 {
 	struct ipmi_smi *intf;
-	int nt = 0;
+	int nt = 0, index;
 
 	if (atomic_read(&stop_operation))
 		return;
 
-	rcu_read_lock();
+	index = srcu_read_lock(&ipmi_interfaces_srcu);
 	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
 		int lnt = 0;
 
@@ -4850,7 +4920,7 @@ static void ipmi_timeout(struct timer_list *unused)
 
 		nt += lnt;
 	}
-	rcu_read_unlock();
+	srcu_read_unlock(&ipmi_interfaces_srcu, index);
 
 	if (nt)
 		mod_timer(&ipmi_timer, jiffies + IPMI_TIMEOUT_JIFFIES);