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re: kern/46648: disconnecting usb mouse crashes system

> | hmmmm, this problem looks pretty annoying, and might affect many
> | devices.  the problem seems to be that:
> | 
> |     - device was pulled out with active transfers
> | 
> |     - the handling of an error in the transfer callback function
> |     is to call usbd_clear_endpoint_stall_async(), which then
> |     sends a clear endpoint transfer
> | 
> |     - adapter transfer list is empty, causing kmem_alloc call,
> |     triggering the assertion since this is happening from the
> |     softintr thread
> | 
> | this idiom is used in many of the USB drivers, so a solution that
> | does not require each one changing seems appropriate.
> | 
> | i'm not sure yet exactly the right answer.  it's clear to me (and
> | has been or a while, since before usbmp) that the USB softintr
> | does way too much work.
> Have a pre-allocated xfer to be used on disconnect. Does this need
> to be per driver or per bus?

if only it were that simple.  the layering makes this
pretty ugly to consider.

i think usbd_clear_endpoint_stall_async() can be changed
to use the usb task thread to send the message.

then the handful of usbd_clear_endpoint_stall() may need
help, but it should fix this case.


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