drivers/net: caif: fix wrong rtnl_is_locked() usage

rtnl_is_locked() doesn't check who holds this lock, it just tells that it's
locked right now. if caif::ldisc_close really can be called under rtrnl_lock
then it should release net device in other context because there is no way
to grab rtnl_lock without deadlock.

This patch adds work which releases these devices. Also this patch fixes calling
dev_close/unregister_netdevice without rtnl_lock from caif_ser_exit().

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Dmitry Tarnyagin <dmitry.tarnyagin@lockless.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 39 insertions, 22 deletions

diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index 77be3cb0b5fe..34dea95d58db 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -35,8 +35,9 @@ MODULE_ALIAS_LDISC(N_CAIF);
 #define OFF 0
 #define CAIF_MAX_MTU 4096
 
-/*This list is protected by the rtnl lock. */
+static DEFINE_SPINLOCK(ser_lock);
 static LIST_HEAD(ser_list);
+static LIST_HEAD(ser_release_list);
 
 static bool ser_loop;
 module_param(ser_loop, bool, S_IRUGO);
@@ -308,6 +309,28 @@ static void ldisc_tx_wakeup(struct tty_struct *tty)
 }
 
 
+static void ser_release(struct work_struct *work)
+{
+        struct list_head list;
+        struct ser_device *ser, *tmp;
+
+        spin_lock(&ser_lock);
+        list_replace_init(&ser_release_list, &list);
+        spin_unlock(&ser_lock);
+
+        if (!list_empty(&list)) {
+                rtnl_lock();
+                list_for_each_entry_safe(ser, tmp, &list, node) {
+                        dev_close(ser->dev);
+                        unregister_netdevice(ser->dev);
+                        debugfs_deinit(ser);
+                }
+                rtnl_unlock();
+        }
+}
+
+static DECLARE_WORK(ser_release_work, ser_release);
+
 static int ldisc_open(struct tty_struct *tty)
 {
         struct ser_device *ser;
@@ -321,6 +344,9 @@ static int ldisc_open(struct tty_struct *tty)
         if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_TTY_CONFIG))
                 return -EPERM;
 
+        /* release devices to avoid name collision */
+        ser_release(NULL);
+
         sprintf(name, "cf%s", tty->name);
         dev = alloc_netdev(sizeof(*ser), name, caifdev_setup);
         if (!dev)
@@ -341,7 +367,9 @@ static int ldisc_open(struct tty_struct *tty)
                 return -ENODEV;
         }
 
+        spin_lock(&ser_lock);
         list_add(&ser->node, &ser_list);
+        spin_unlock(&ser_lock);
         rtnl_unlock();
         netif_stop_queue(dev);
         update_tty_status(ser);
@@ -351,19 +379,13 @@ static int ldisc_open(struct tty_struct *tty)
 static void ldisc_close(struct tty_struct *tty)
 {
         struct ser_device *ser = tty->disc_data;
-        /* Remove may be called inside or outside of rtnl_lock */
-        int islocked = rtnl_is_locked();
 
-        if (!islocked)
-                rtnl_lock();
-        /* device is freed automagically by net-sysfs */
-        dev_close(ser->dev);
-        unregister_netdevice(ser->dev);
-        list_del(&ser->node);
-        debugfs_deinit(ser);
         tty_kref_put(ser->tty);
-        if (!islocked)
-                rtnl_unlock();
+
+        spin_lock(&ser_lock);
+        list_move(&ser->node, &ser_release_list);
+        spin_unlock(&ser_lock);
+        schedule_work(&ser_release_work);
 }
 
 /* The line discipline structure. */
@@ -438,16 +460,11 @@ static int __init caif_ser_init(void)
 
 static void __exit caif_ser_exit(void)
 {
-        struct ser_device *ser = NULL;
-        struct list_head *node;
-        struct list_head *_tmp;
-
-        list_for_each_safe(node, _tmp, &ser_list) {
-                ser = list_entry(node, struct ser_device, node);
-                dev_close(ser->dev);
-                unregister_netdevice(ser->dev);
-                list_del(node);
-        }
+        spin_lock(&ser_lock);
+        list_splice(&ser_list, &ser_release_list);
+        spin_unlock(&ser_lock);
+        ser_release(NULL);
+        cancel_work_sync(&ser_release_work);
         tty_unregister_ldisc(N_CAIF);
         debugfs_remove_recursive(debugfsdir);
 }