wimax/i2400m: fix oops caused by race condition when exiting USB kthreads

Current i2400m USB code had to threads (one for processing RX, one for
TX). When calling i2400m_{tx,rx}_release(), it would crash if the
thread had exited already due to an error.

So changed the code to have the thread fill in/out
i2400mu->{tx,rx}_kthread under a spinlock; then the _release()
function will call kthread_stop() only if {rx,tx}_kthread is still
set.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>

1 files changed, 30 insertions, 5 deletions

diff --git a/drivers/net/wimax/i2400m/usb-tx.c b/drivers/net/wimax/i2400m/usb-tx.c
index 90dfff1afb8a..a3c46e99c804 100644
--- a/drivers/net/wimax/i2400m/usb-tx.c
+++ b/drivers/net/wimax/i2400m/usb-tx.c
@@ -161,9 +161,15 @@ int i2400mu_txd(void *_i2400mu)
         struct device *dev = &i2400mu->usb_iface->dev;
         struct i2400m_msg_hdr *tx_msg;
         size_t tx_msg_size;
+        unsigned long flags;
 
         d_fnstart(4, dev, "(i2400mu %p)\n", i2400mu);
 
+        spin_lock_irqsave(&i2400m->tx_lock, flags);
+        BUG_ON(i2400mu->tx_kthread != NULL);
+        i2400mu->tx_kthread = current;
+        spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+
         while (1) {
                 d_printf(2, dev, "TX: waiting for messages\n");
                 tx_msg = NULL;
@@ -183,6 +189,11 @@ int i2400mu_txd(void *_i2400mu)
                 if (result < 0)
                         break;
         }
+
+        spin_lock_irqsave(&i2400m->tx_lock, flags);
+        i2400mu->tx_kthread = NULL;
+        spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+
         d_fnend(4, dev, "(i2400mu %p) = %d\n", i2400mu, result);
         return result;
 }
@@ -213,11 +224,13 @@ int i2400mu_tx_setup(struct i2400mu *i2400mu)
         struct i2400m *i2400m = &i2400mu->i2400m;
         struct device *dev = &i2400mu->usb_iface->dev;
         struct wimax_dev *wimax_dev = &i2400m->wimax_dev;
+        struct task_struct *kthread;
 
-        i2400mu->tx_kthread = kthread_run(i2400mu_txd, i2400mu, "%s-tx",
-                                          wimax_dev->name);
-        if (IS_ERR(i2400mu->tx_kthread)) {
-                result = PTR_ERR(i2400mu->tx_kthread);
+        kthread = kthread_run(i2400mu_txd, i2400mu, "%s-tx",
+                              wimax_dev->name);
+        /* the kthread function sets i2400mu->tx_thread */
+        if (IS_ERR(kthread)) {
+                result = PTR_ERR(kthread);
                 dev_err(dev, "TX: cannot start thread: %d\n", result);
         }
         return result;
@@ -225,5 +238,17 @@ int i2400mu_tx_setup(struct i2400mu *i2400mu)
 
 void i2400mu_tx_release(struct i2400mu *i2400mu)
 {
-        kthread_stop(i2400mu->tx_kthread);
+        unsigned long flags;
+        struct i2400m *i2400m = &i2400mu->i2400m;
+        struct device *dev = i2400m_dev(i2400m);
+        struct task_struct *kthread;
+
+        spin_lock_irqsave(&i2400m->tx_lock, flags);
+        kthread = i2400mu->tx_kthread;
+        i2400mu->tx_kthread = NULL;
+        spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+        if (kthread)
+                kthread_stop(kthread);
+        else
+                d_printf(1, dev, "TX: kthread had already exited\n");
 }