RELENG7 using lpt causes panic

John Baldwin jhb at
Mon Jan 7 21:12:47 PST 2008

On Monday 07 January 2008 10:08:57 pm Adrian Wontroba wrote:
> I've recently switched some of my home systems to RELENG7.
> All seemed fairly well until I tried printing a CUPS test page on my
> backup and print server to an elderly Laserjet IIIp, where I seem to
> have a reproducible panic. It has happened twice.  This is painful, as
> I have a big home fileystem (striped over two mirrors over most of two
> 500 GB disks). The gmirror syncronisation and background fsck leave the
> system close to unusable for hours while they fight over the disks.
> I was somewhat startled that something so basic as printing causes a
> panic. There have been no hardware changes since I last printed under
> RELENG6, but I don't print often, so hardware decay is a possibility.
> Is this a known problem? If not, I'll take the time to try various tests
> (with /home unmounted) and raise a PR.
> I envisage tests such as:
> * Does switching to a kernel without SMP and apic make a difference?
> * Does direct output cause a crash?
> * Does polling make a difference?
> * Does the parallel port mode (I think extended at present) make a
>   difference?
> Some detail below.

This is a known issue and it has to do with some changes in the interrupt
code in 7.x that interact badly with the lpt(4) driver (which tears down its
interrupt handler and sets it back up again for each character, and the
panic you see is because an interrupt came when it wasn't expecting it).
The lpt(4) driver does this weird dance to allow coexisting with vpo so you
can have lpd running and unplug your printer and plug up a Zip drive w/o
having to stop lpd.  I think the way I want to fix it is to change the lpt
driver to not release the bus (and thus remove its interrupt handler) for
every char but to keep the bus while /dev/lpt0 is open (which would be all
the time with lpd running).

John Baldwin

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