rtlwifi: rtl8192cu: Change buffer allocation for synchronous reads

In commit a7959c1, the USB part of rtlwifi was switched to convert
_usb_read_sync() to using a preallocated buffer rather than one
that has been acquired using kmalloc. Although this routine is named
as though it were synchronous, there seem to be simultaneous users,
and the selection of the index to the data buffer is not multi-user
safe. This situation is addressed by adding a new spinlock. The routine
cannot sleep, thus a mutex is not allowed.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/net/wireless/rtlwifi/usb.c b/drivers/net/wireless/rtlwifi/usb.c
index a6049d7d51b3..aa970fc18a21 100644
--- a/drivers/net/wireless/rtlwifi/usb.c
+++ b/drivers/net/wireless/rtlwifi/usb.c
@@ -131,15 +131,19 @@ static u32 _usb_read_sync(struct rtl_priv *rtlpriv, u32 addr, u16 len)
         u8 request;
         u16 wvalue;
         u16 index;
-        __le32 *data = &rtlpriv->usb_data[rtlpriv->usb_data_index];
+        __le32 *data;
+        unsigned long flags;
 
+        spin_lock_irqsave(&rtlpriv->locks.usb_lock, flags);
+        if (++rtlpriv->usb_data_index >= RTL_USB_MAX_RX_COUNT)
+                rtlpriv->usb_data_index = 0;
+        data = &rtlpriv->usb_data[rtlpriv->usb_data_index];
+        spin_unlock_irqrestore(&rtlpriv->locks.usb_lock, flags);
         request = REALTEK_USB_VENQT_CMD_REQ;
         index = REALTEK_USB_VENQT_CMD_IDX; /* n/a */
 
         wvalue = (u16)addr;
         _usbctrl_vendorreq_sync_read(udev, request, wvalue, index, data, len);
-        if (++rtlpriv->usb_data_index >= RTL_USB_MAX_RX_COUNT)
-                rtlpriv->usb_data_index = 0;
         return le32_to_cpu(*data);
 }
 
@@ -951,6 +955,10 @@ int __devinit rtl_usb_probe(struct usb_interface *intf,
                                     GFP_KERNEL);
         if (!rtlpriv->usb_data)
                 return -ENOMEM;
+
+        /* this spin lock must be initialized early */
+        spin_lock_init(&rtlpriv->locks.usb_lock);
+
         rtlpriv->usb_data_index = 0;
         init_completion(&rtlpriv->firmware_loading_complete);
         SET_IEEE80211_DEV(hw, &intf->dev);