Bluetooth: btusb: Fix race when waiting for BTUSB_DOWNLOADING

The test for BTUSB_DOWNLOADING must be after adding to the wait queue
and setting the TASK_INTERRUPTIBLE state. Otherwise the flag may get
cleared after we test for it and we end up getting a timeout since
schedule_timeout() waits for the full duration. This patch uses a
wait_on_bit_timeout() + wake_up_bit(). To perform the task both
race-free as well as in a much simpler way.

Since there's no global wait_on_bit_timeout() helper yet (even though
all the building blocks for it are in place) this patch creates a
temporary local btusb copy of it until the global one has made it to
upstream trees.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 34 insertions, 33 deletions

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index 86f3d92de22a..98341a463f30 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -334,6 +334,16 @@ struct btusb_data {
         int (*recv_bulk)(struct btusb_data *data, void *buffer, int count);
 };
 
+static int btusb_wait_on_bit_timeout(void *word, int bit, unsigned long timeout,
+                                     unsigned mode)
+{
+        might_sleep();
+        if (!test_bit(bit, word))
+                return 0;
+        return out_of_line_wait_on_bit_timeout(word, bit, bit_wait_timeout,
+                                               mode, timeout);
+}
+
 static inline void btusb_free_frags(struct btusb_data *data)
 {
         unsigned long flags;
@@ -1800,8 +1810,10 @@ static int btusb_recv_event_intel(struct hci_dev *hdev, struct sk_buff *skb)
 
                         if (test_and_clear_bit(BTUSB_DOWNLOADING,
                                                &data->flags) &&
-                            test_bit(BTUSB_FIRMWARE_LOADED, &data->flags))
-                                wake_up_interruptible(&hdev->req_wait_q);
+                            test_bit(BTUSB_FIRMWARE_LOADED, &data->flags)) {
+                                smp_mb__after_atomic();
+                                wake_up_bit(&data->flags, BTUSB_DOWNLOADING);
+                        }
                 }
 
                 /* When switching to the operational firmware the device
@@ -2165,43 +2177,32 @@ static int btusb_setup_intel_new(struct hci_dev *hdev)
 
         set_bit(BTUSB_FIRMWARE_LOADED, &data->flags);
 
+        BT_INFO("%s: Waiting for firmware download to complete", hdev->name);
+
         /* Before switching the device into operational mode and with that
          * booting the loaded firmware, wait for the bootloader notification
          * that all fragments have been successfully received.
          *
-         * When the event processing receives the notification, then this
-         * flag will be cleared. So just in case that happens really quickly,
-         * check it first before adding the wait queue.
+         * When the event processing receives the notification, then the
+         * BTUSB_DOWNLOADING flag will be cleared.
+         *
+         * The firmware loading should not take longer than 5 seconds
+         * and thus just timeout if that happens and fail the setup
+         * of this device.
          */
-        if (test_bit(BTUSB_DOWNLOADING, &data->flags)) {
-                DECLARE_WAITQUEUE(wait, current);
-                signed long timeout;
-
-                BT_INFO("%s: Waiting for firmware download to complete",
-                        hdev->name);
-
-                add_wait_queue(&hdev->req_wait_q, &wait);
-                set_current_state(TASK_INTERRUPTIBLE);
-
-                /* The firmware loading should not take longer than 5 seconds
-                 * and thus just timeout if that happens and fail the setup
-                 * of this device.
-                 */
-                timeout = schedule_timeout(msecs_to_jiffies(5000));
-
-                remove_wait_queue(&hdev->req_wait_q, &wait);
-
-                if (signal_pending(current)) {
-                        BT_ERR("%s: Firmware loading interrupted", hdev->name);
-                        err = -EINTR;
-                        goto done;
-                }
+        err = btusb_wait_on_bit_timeout(&data->flags, BTUSB_DOWNLOADING,
+                                        msecs_to_jiffies(5000),
+                                        TASK_INTERRUPTIBLE);
+        if (err == 1) {
+                BT_ERR("%s: Firmware loading interrupted", hdev->name);
+                err = -EINTR;
+                goto done;
+        }
 
-                if (!timeout) {
-                        BT_ERR("%s: Firmware loading timeout", hdev->name);
-                        err = -ETIMEDOUT;
-                        goto done;
-                }
+        if (err) {
+                BT_ERR("%s: Firmware loading timeout", hdev->name);
+                err = -ETIMEDOUT;
+                goto done;
         }
 
         if (test_bit(BTUSB_FIRMWARE_FAILED, &data->flags)) {