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SubjectRe: 2.6.31-rc5 regression: Oops when USB Serial disconnected while in use
On Sat, 22 Aug 2009, Alan Stern wrote:

> Alan:
>
> There's a problem with the tty->ops->shutdown method. It needs to
> release the last port reference owned by the current tty. But when was
> that reference originally acquired? Evidently during the first time
> serial_open() was called for the current tty.
>
> The problem is that serial_open() has no way to know if a particular
> invocation is the first one for this tty! The ASYNCB_INITIALIZED flag
> doesn't help, because it might not get set during the first call (i.e.,
> if an error occurs).
>
> To do this right, we need a flag in the tty_struct or the tty_port
> which serial_open() can set when acquiring that first reference and
> shutdown method can clear. Should I add such a flag?

Never mind, I figured out an answer. Instead of a new flag, the
routine can simply test whether or not tty->driver_data has been set.

One more question: Under what circumstances should serial_open()
increment port->port.count? It seems that this should happen on every
call unless tty->driver_data is NULL or filp has been hung up. Is that
right?

I have a big patch almost ready for testing. Unfortunately I don't
have access to my usual hardware right now, so I can't test it until
the middle of the week. Bruno, if you like I will send you the patch
when it looks okay and you can try it out.

Alan Stern



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