Re: panic: device_unbusy: called for non-busy device iichid0

On 27.05.2021 14:41, David Wolfskill wrote:
> This was on the new(er) laptop with which I have been experimenting; it
> uses iichid to controll/access the built-in mouse/touchpad.
> 
> The machine was running:
> 
> FreeBSD g1-48.catwhisker.org 14.0-CURRENT FreeBSD 14.0-CURRENT #252 main-n246951-38e7025a60b2: Wed May 26 04:56:25 PDT 2021     root@g1-48.catwhisker.org:/common/S4/obj/usr/src/amd64.amd64/sys/CANARY  amd64 1400017 1400017
> 
> at the time.  Note that the reboot after building the above (yesterday)
> was without issue, and the reboot after the panic was also without issue
> -- so this would seem to have elements of timing/racing involved.  (And
> it's likely to be distinctly unpleasant to debug, as it seems that
> reproduction may be rather "iffy.")
> 
> I took a photo of the displayed backtrace; it's at
> https://www.catwhisker.org/~david/FreeBSD/head/n246951/device_unbusy.jpg
> 
> Here's a slightly-abbreviated hand-transcribed version:
> 
> panic: device_unbusy: called for non-busy device iichid0
> cpuid = 8
> time = 1622113818
> KDB: stack backtrace:
> db_trace_self_wrapper()
> vpanic()
> panic()
> device_unbusy()
> iicbus_release_bus()
> iichid_intr()
> ithread-loop()
> fork_exit()
> fork_trampoline()
> --- trap 0, rip = 0, rsp = 0, rbp = 0 ---
> KDB: enter: panic
> [ thread pid 12 tid 100170 ]
> Stopped at      0xffffffff80c36867 = kdb_enter+ 0x37:    $0,0x12a0b9e(%rip)
> db> 
> 

It looks like iicbus issue.

It was very easy reproducible with iichid when latter had a bug
triggering interrupt storm on device_attach:

https://github.com/wulf7/iichid/issues/22

It was caused by unlocked calls to device_busy() and device_unbusy() in
iicbus_request_bus() routine. These unlocked calls resulted in races
with parallel device attachment process.

CC-ed ian@

-- 
WBR
Vladimir Kondratyev