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To: koitsu@freebsd.org
From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: freebsd-stable@freebsd.org, freebsd-usb@freebsd.org
Subject: Re: USB to RS232 converter problem (prolific chip)
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In message: <20080405215838.GA27195@eos.sc1.parodius.com>
            Jeremy Chadwick <koitsu@freebsd.org> writes:
: Bottom line: the current FreeBSD USB stack is very fragile and
: unreliable.  You may want to try the usb4bsd kernel patches (I think
: that's what it's called), some have had better luck with those.  Search
: the web.

This crash has nothing to do with the usb stack.  The root cause is
the device deletion code nulls out a pointer.  There's a routine that
is sleeping which is woken up and the null pointer gets dereferenced
leading to the crash.

The current usb stack isn't as fragile as it was in the 5.x days.
While there are problems, this one isn't due to that.  The same thing
happens when you eject a PC Card 16550 COM device, due to the same
bug.

Warner