On Wed, 2010-08-04 at 07:03 -0500, Jason Wessel wrote:

The usb serial has the same kind of problem with all sorts of locks.
I
had resorted to using a tasklet or workqueue to get the sysrq to
execute
just outside the usb serial driver context.  This work never made it
upstream because it was part of another series, but the reference is:
http://lkml.org/lkml/2010/3/9/17

For the standard serial you might be able to get away with dropping
the
lock for the sysrq.

Did you have a particular way to trigger the problem or was it just
completely random, because I don't know that I have observed this
behavior with the typical 8250 driver.

Yes, I do actually :-) A 64-way machine and a bunch of processes
flooding the console will do it just fine :-)

Cheers,
Ben.