wimax/i2400m: fix oops in TX when tearing down the device

All the entry points into the TX module should check if the device has
been torn down. Otherwise, when the device resets or shuts down, there
are windows when a call to i2400m_tx*() will oops the system.

For that, make i2400m_tx_release() set i2400m->tx_buf to NULL under
the tx_lock. Then, any entry point [i2400m_tx(), _tx_msg_sent(),
_tx_msg_get()] will check for i2400m->tx_buf to be NULL and exit
gracefully.

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

drivers/net/wimax/i2400m/sdio-tx.c

@@ -149,5 +149,8 @@ int i2400ms_tx_setup(struct i2400ms *i2400ms)
 
 void i2400ms_tx_release(struct i2400ms *i2400ms)
 {
-	destroy_workqueue(i2400ms->tx_workqueue);
+	if (i2400ms->tx_workqueue) {
+		destroy_workqueue(i2400ms->tx_workqueue);
+		i2400ms->tx_workqueue = NULL;
+	}
 }

drivers/net/wimax/i2400m/tx.c

@@ -642,6 +642,9 @@ int i2400m_tx(struct i2400m *i2400m, const void *buf, size_t buf_len,
 	 * current one is out of payload slots or we have a singleton,
 	 * close it and start a new one */
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	result = -ESHUTDOWN;
+	if (i2400m->tx_buf == NULL)
+		goto error_tx_new;
 try_new:
 	if (unlikely(i2400m->tx_msg == NULL))
 		i2400m_tx_new(i2400m);
@@ -697,7 +700,10 @@ int i2400m_tx(struct i2400m *i2400m, const void *buf, size_t buf_len,
 	}
 error_tx_new:
 	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
-	i2400m->bus_tx_kick(i2400m);	/* always kick, might free up space */
+	/* kick in most cases, except when the TX subsys is down, as
+	 * it might free space */
+	if (likely(result != -ESHUTDOWN))
+		i2400m->bus_tx_kick(i2400m);
 	d_fnend(3, dev, "(i2400m %p skb %p [%zu bytes] pt %u) = %d\n",
 		i2400m, buf, buf_len, pl_type, result);
 	return result;
@@ -740,6 +746,9 @@ struct i2400m_msg_hdr *i2400m_tx_msg_get(struct i2400m *i2400m,
 
 	d_fnstart(3, dev, "(i2400m %p bus_size %p)\n", i2400m, bus_size);
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	tx_msg_moved = NULL;
+	if (i2400m->tx_buf == NULL)
+		goto out_unlock;
 skip:
 	tx_msg_moved = NULL;
 	if (i2400m->tx_in == i2400m->tx_out) {	/* Empty FIFO? */
@@ -829,6 +838,8 @@ void i2400m_tx_msg_sent(struct i2400m *i2400m)
 
 	d_fnstart(3, dev, "(i2400m %p)\n", i2400m);
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	if (i2400m->tx_buf == NULL)
+		goto out_unlock;
 	i2400m->tx_out += i2400m->tx_msg_size;
 	d_printf(2, dev, "TX: sent %zu b\n", (size_t) i2400m->tx_msg_size);
 	i2400m->tx_msg_size = 0;
@@ -837,6 +848,7 @@ void i2400m_tx_msg_sent(struct i2400m *i2400m)
 	n = i2400m->tx_out / I2400M_TX_BUF_SIZE;
 	i2400m->tx_out %= I2400M_TX_BUF_SIZE;
 	i2400m->tx_in -= n * I2400M_TX_BUF_SIZE;
+out_unlock:
 	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
 	d_fnend(3, dev, "(i2400m %p) = void\n", i2400m);
 }
@@ -876,5 +888,9 @@ int i2400m_tx_setup(struct i2400m *i2400m)
  */
 void i2400m_tx_release(struct i2400m *i2400m)
 {
+	unsigned long flags;
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
 	kfree(i2400m->tx_buf);
+	i2400m->tx_buf = NULL;
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
 }