aac / ld interaction

[Havard Eidnes <he%NetBSD.org@localhost>]

Hi,

this afternoon I attempted to upgrade NetBSD from 7.1_STABLE to
8.0_BETA on an amd64-running machine in our lab.  It has an aac
controller, probed like so:

aac0 at pci6 dev 0 function 0: IBM ServeRAID 8k
aac0: interrupting at ioapic0 pin 17
aac0: Enabling 64-bit address support
aac0: Enable 64-bit array support
aac0: New comm. interface enabled
aac0: MIPS 5KC at 250MHz, 32MB mem (16MB cache), optional battery not installed
ld0 at aac0 unit 0: RAID 1 (Mirror)
ld0: 232 GB, 30378 cyl, 255 head, 63 sec, 512 bytes/sect x 488036352 sectors
ld1 at aac0 unit 1: RAID 10
ld1: 465 GB, 60757 cyl, 255 head, 63 sec, 512 bytes/sect x 976072704 sectors

Apparently, somewhere between those two kernel versions, the 'ld'
driver was MPified, while the aac driver was not.

The symptom I noticed this with was that I managed to unpack the
'base' set from the 8.0_BETA build, but 29% into the 'comp' set, the
machine decided to panic with a rather mysterious null pointer
de-reference inside the aac driver, pointing (by the looks of it) to
the SIMPLEQ_FIRST macro use inside aac_ccb_enqueue().

By this time I had a machine with an 8-based user-land but with a
brittle 8 kernel, and of course the 7-based kernel doesn't want
anything to do with the 8-based ifconfig, so by the looks of it, the
machine is going to need me to physically visit it to rescue it out of
this bind, even though I have remote serial console.

I don't know the MPify-state for the other sub-drivers under 'ld'
(I see aac, cac, icp, mlx and nvme), but this should probably get
some proper attention before 8.0 is released...

And, I have it on good authority that simply replacing splbio() /
splx() with mutex_enter() / mutex_exit() isn't going to work, because
there are a number of things which are not permitted in a mutex-based
critical section which are perfectly fine in an splbio()-protected
section, such as doing malloc(), using bus_* functions etc. etc.  So
the conversion is decidedly not trivial, and certainly above my
current skill level.

So, "Help!"

Regards,

- Håvard