As David VomLehn points out, it was possible to receive an interrupt
before clearing the free-urb flag which could lead to the urb being
incorrectly marked as busy.
For the same reason, move tx_bytes accounting so that it will never be
negative.
Note that the free-flags set and clear operations do not need any
additional locking as they are manipulated while USB_SERIAL_WRITE_BUSY
is set.
Reported-by: David VomLehn <dvomlehn@xxxxxxxxx>
Signed-off-by: Johan Hovold <jhovold@xxxxxxxxx>
---
Hi,
I was able to trigger the bug David identified by simply inserting a delay
after submit_urb, and I have also verified that the patch below solves the
problem.
Note that the set/clear bit operations below do not need any additional
locking as the write-busy flag is set.
Thanks,
Johan
drivers/usb/serial/generic.c | 15 ++++++++++-----
1 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index a817ced..ca92f67 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -208,18 +208,23 @@ retry:
urb->transfer_buffer_length = count;
usb_serial_debug_data(debug, &port->dev, __func__, count,
urb->transfer_buffer);
+ spin_lock_irqsave(&port->lock, flags);
+ port->tx_bytes += count;
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ clear_bit(i, &port->write_urbs_free);
result = usb_submit_urb(urb, GFP_ATOMIC);
if (result) {
dev_err(&port->dev, "%s - error submitting urb: %d\n",
__func__, result);
+ set_bit(i, &port->write_urbs_free);
+ spin_lock_irqsave(&port->lock, flags);
+ port->tx_bytes -= count;
+ spin_unlock_irqrestore(&port->lock, flags);
+
clear_bit_unlock(USB_SERIAL_WRITE_BUSY, &port->flags);
return result;
}
- clear_bit(i, &port->write_urbs_free);
-
- spin_lock_irqsave(&port->lock, flags);
- port->tx_bytes += count;
- spin_unlock_irqrestore(&port->lock, flags);
/* Try sending off another urb, unless in irq context (in which case
* there will be no free urb). */
--
1.7.1.1
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