rt2x00: Place mutex around USB register access

There is a buffer, csr_cache which is used to hold copies of data being passed
to the USB stack which can get corrupted if multiple threads attempt to access
CSR registers simultaneously. There is also the possibility if multiple
threads try to access BBP or RF registers for the multiple USB operations
needed to get interleaved leading to incorrect results. This patch introduces
a mutex to prevent such simultaneous access. The interleaved access problem
may also affect the PCI devices but if so that will be handled in a follow-up
patch.

Signed-off-by: Adam Baker <linux@baker-net.org.uk>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 45 insertions, 7 deletions

diff --git a/drivers/net/wireless/rt2x00/rt2500usb.c b/drivers/net/wireless/rt2x00/rt2500usb.c
index c89103786b1c..a00420e9626b 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -52,6 +52,8 @@
  * between each attampt. When the busy bit is still set at that time,
  * the access attempt is considered to have failed,
  * and we will print an error.
+ * If the usb_cache_mutex is already held then the _lock variants must
+ * be used instead.
  */
 static inline void rt2500usb_register_read(struct rt2x00_dev *rt2x00dev,
                                            const unsigned int offset,
@@ -64,6 +66,17 @@ static inline void rt2500usb_register_read(struct rt2x00_dev *rt2x00dev,
         *value = le16_to_cpu(reg);
 }
 
+static inline void rt2500usb_register_read_lock(struct rt2x00_dev *rt2x00dev,
+                                                const unsigned int offset,
+                                                u16 *value)
+{
+        __le16 reg;
+        rt2x00usb_vendor_req_buff_lock(rt2x00dev, USB_MULTI_READ,
+                                       USB_VENDOR_REQUEST_IN, offset,
+                                       &reg, sizeof(u16), REGISTER_TIMEOUT);
+        *value = le16_to_cpu(reg);
+}
+
 static inline void rt2500usb_register_multiread(struct rt2x00_dev *rt2x00dev,
                                                 const unsigned int offset,
                                                 void *value, const u16 length)
@@ -84,6 +97,16 @@ static inline void rt2500usb_register_write(struct rt2x00_dev *rt2x00dev,
                                       &reg, sizeof(u16), REGISTER_TIMEOUT);
 }
 
+static inline void rt2500usb_register_write_lock(struct rt2x00_dev *rt2x00dev,
+                                                 const unsigned int offset,
+                                                 u16 value)
+{
+        __le16 reg = cpu_to_le16(value);
+        rt2x00usb_vendor_req_buff_lock(rt2x00dev, USB_MULTI_WRITE,
+                                       USB_VENDOR_REQUEST_OUT, offset,
+                                       &reg, sizeof(u16), REGISTER_TIMEOUT);
+}
+
 static inline void rt2500usb_register_multiwrite(struct rt2x00_dev *rt2x00dev,
                                                  const unsigned int offset,
                                                  void *value, const u16 length)
@@ -100,7 +123,7 @@ static u16 rt2500usb_bbp_check(struct rt2x00_dev *rt2x00dev)
         unsigned int i;
 
         for (i = 0; i < REGISTER_BUSY_COUNT; i++) {
-                rt2500usb_register_read(rt2x00dev, PHY_CSR8, &reg);
+                rt2500usb_register_read_lock(rt2x00dev, PHY_CSR8, &reg);
                 if (!rt2x00_get_field16(reg, PHY_CSR8_BUSY))
                         break;
                 udelay(REGISTER_BUSY_DELAY);
@@ -114,12 +137,15 @@ static void rt2500usb_bbp_write(struct rt2x00_dev *rt2x00dev,
 {
         u16 reg;
 
+        mutex_lock(&rt2x00dev->usb_cache_mutex);
+
         /*
          * Wait until the BBP becomes ready.
          */
         reg = rt2500usb_bbp_check(rt2x00dev);
         if (rt2x00_get_field16(reg, PHY_CSR8_BUSY)) {
                 ERROR(rt2x00dev, "PHY_CSR8 register busy. Write failed.\n");
+                mutex_unlock(&rt2x00dev->usb_cache_mutex);
                 return;
         }
 
@@ -131,7 +157,9 @@ static void rt2500usb_bbp_write(struct rt2x00_dev *rt2x00dev,
         rt2x00_set_field16(&reg, PHY_CSR7_REG_ID, word);
         rt2x00_set_field16(&reg, PHY_CSR7_READ_CONTROL, 0);
 
-        rt2500usb_register_write(rt2x00dev, PHY_CSR7, reg);
+        rt2500usb_register_write_lock(rt2x00dev, PHY_CSR7, reg);
+
+        mutex_unlock(&rt2x00dev->usb_cache_mutex);
 }
 
 static void rt2500usb_bbp_read(struct rt2x00_dev *rt2x00dev,
@@ -139,6 +167,8 @@ static void rt2500usb_bbp_read(struct rt2x00_dev *rt2x00dev,
 {
         u16 reg;
 
+        mutex_lock(&rt2x00dev->usb_cache_mutex);
+
         /*
          * Wait until the BBP becomes ready.
          */
@@ -155,7 +185,7 @@ static void rt2500usb_bbp_read(struct rt2x00_dev *rt2x00dev,
         rt2x00_set_field16(&reg, PHY_CSR7_REG_ID, word);
         rt2x00_set_field16(&reg, PHY_CSR7_READ_CONTROL, 1);
 
-        rt2500usb_register_write(rt2x00dev, PHY_CSR7, reg);
+        rt2500usb_register_write_lock(rt2x00dev, PHY_CSR7, reg);
 
         /*
          * Wait until the BBP becomes ready.
@@ -164,11 +194,14 @@ static void rt2500usb_bbp_read(struct rt2x00_dev *rt2x00dev,
         if (rt2x00_get_field16(reg, PHY_CSR8_BUSY)) {
                 ERROR(rt2x00dev, "PHY_CSR8 register busy. Read failed.\n");
                 *value = 0xff;
+                mutex_unlock(&rt2x00dev->usb_cache_mutex);
                 return;
         }
 
-        rt2500usb_register_read(rt2x00dev, PHY_CSR7, &reg);
+        rt2500usb_register_read_lock(rt2x00dev, PHY_CSR7, &reg);
         *value = rt2x00_get_field16(reg, PHY_CSR7_DATA);
+
+        mutex_unlock(&rt2x00dev->usb_cache_mutex);
 }
 
 static void rt2500usb_rf_write(struct rt2x00_dev *rt2x00dev,
@@ -180,20 +213,23 @@ static void rt2500usb_rf_write(struct rt2x00_dev *rt2x00dev,
         if (!word)
                 return;
 
+        mutex_lock(&rt2x00dev->usb_cache_mutex);
+
         for (i = 0; i < REGISTER_BUSY_COUNT; i++) {
-                rt2500usb_register_read(rt2x00dev, PHY_CSR10, &reg);
+                rt2500usb_register_read_lock(rt2x00dev, PHY_CSR10, &reg);
                 if (!rt2x00_get_field16(reg, PHY_CSR10_RF_BUSY))
                         goto rf_write;
                 udelay(REGISTER_BUSY_DELAY);
         }
 
+        mutex_unlock(&rt2x00dev->usb_cache_mutex);
         ERROR(rt2x00dev, "PHY_CSR10 register busy. Write failed.\n");
         return;
 
 rf_write:
         reg = 0;
         rt2x00_set_field16(&reg, PHY_CSR9_RF_VALUE, value);
-        rt2500usb_register_write(rt2x00dev, PHY_CSR9, reg);
+        rt2500usb_register_write_lock(rt2x00dev, PHY_CSR9, reg);
 
         reg = 0;
         rt2x00_set_field16(&reg, PHY_CSR10_RF_VALUE, value >> 16);
@@ -201,8 +237,10 @@ rf_write:
         rt2x00_set_field16(&reg, PHY_CSR10_RF_IF_SELECT, 0);
         rt2x00_set_field16(&reg, PHY_CSR10_RF_BUSY, 1);
 
-        rt2500usb_register_write(rt2x00dev, PHY_CSR10, reg);
+        rt2500usb_register_write_lock(rt2x00dev, PHY_CSR10, reg);
         rt2x00_rf_write(rt2x00dev, word, value);
+
+        mutex_unlock(&rt2x00dev->usb_cache_mutex);
 }
 
 #ifdef CONFIG_RT2X00_LIB_DEBUGFS