Am 29.01.2013 11:35, schrieb Alexander Holler:

Am 29.01.2013 01:56, schrieb Alexander Holler:

quoted

Am 29.01.2013 01:22, schrieb Andrew Morton:

quoted

On Fri, 25 Jan 2013 19:49:27 +0100
Alexander Holler [off-list ref] wrote:

quoted

When a device was disconnected the driver may hang at waiting for
urbs it never
will get. Fix this by using a timeout while waiting for the used
semaphore.

There is still a memory leak if a timeout happens, but at least the
driver
now continues his disconnect routine.

...

--- a/drivers/video/udlfb.c
+++ b/drivers/video/udlfb.c

@@ -1832,8 +1832,9 @@ static void dlfb_free_urb_list(struct

dlfb_data *dev)
      /* keep waiting and freeing, until we've got 'em all */
      while (count--) {

-        /* Getting interrupted means a leak, but ok at disconnect */
-        ret = down_interruptible(&dev->urbs.limit_sem);
+        /* Timeout likely occurs at disconnect (resulting in a
leak) */
+        ret = down_timeout_killable(&dev->urbs.limit_sem,
+                        FREE_URB_TIMEOUT);
          if (ret)
              break;

This is rather a hack.  Do you have an understanding of the underlying
bug?  Why is the driver waiting for things which will never happen?

To add a bit more explanation:

I've experienced that bug after moving the fb-damage-handling into a
workqueue (to make the driver usable as console). This likely has
increased the possibility that an urb gets missed when the usb-stack
calls the (usb-)disconnect function of the driver. But I don't know as I
couldn't use the driver before (as fbcon) so I don't really have a
comparison.

What currently happens here is something like that:

fb -> damage -> workload which sends urb and waits for answer
device disconnect -> dlfb_usb_disconnect() -> stall (no answer to the
above urb)

I don't know why the disconnect waits for all urbs. The code looks like
it does that just to free the allocated memory. As I'm not very familiar
with the usb-stack, I would have to read up about the urb-handling to
find out how to free the memory otherwise.

As the previous comment in the code suggests that urbs already got
missed (on shutdown) before, I assume that even without my patch, which
moved the damage into a workqueue, the problem could occur which then
prevents a shutdown as there is no timeout. As I've experienced that
problem not only on disconnect, but on shutdown too (no shutdown was
possible), I have to assume, that the previous used down_interruptible()
didn't get a signal on shutdown (if the driver is used as fbcon),
therefor I consider the timeout as necessary.

To explain the problem on shutdown a bit further, I think the following 
happens (usb and driver are statically linked and started by the kernel):

shutdown -> kill signal -> usb stack shuts down -> udlfb waits (forever) 
for a kill or an urb which it doesn't get.

Maybe the sequence is different if the usb-stack and udlfb are used as a 
module and/or udlfb is used only for X/fb. I'm not sure what actually 
does shut down the usb-stack in such a case, but maybe more than one 
kill signal might be thrown around.

Regards,

Alexander