pfind() in ithread handler

[Attilio Rao]

2008/2/28, Yuri Pankov <yuri.pankov at gmail.com>:
> Hi,
>
>  I'm trying to understand the cause of following panic.
>
>  panic: Trying sleep, but thread marked as sleeping prohibited
>  cpuid = 0
>  KDB: stack backtrace:
>  db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
>  panic() at panic+0x17d
>  sleepq_add() at sleepq_add+0x2e1
>  _sx_slock_hard() at _sx_slock_hard+0x15d
>  _sx_slock() at _sx_slock+0xc1
>  pfind() at pfind+0x24
>  saa_intr() at saa_intr+0x313
>  ithread_loop() at ithread_loop+0xda
>  fork_exit() at fork_exit+0x12a
>  fork_trampoline() at fork_trampoline+0xe
>  --- trap 0, rip = 0, rsp = 0xffffffffac3c0d30, rbp = 0 ---
>
>  Can someone enlighten me on what is causing the panic and is it ok to
>  use pfind() in interrupt handler (I have very limited understanding of
>  kernel internals)?
>
>  Code in question (taken from saa driver
>  http://freebsd.ricin.com/ports/distfiles/kbtv-1.92.tbz) can be found at
>  http://www.pastebin.ca/921830

ithreads cannot perform unbound sleeps and pfind() needs to access to
allproc_lock which is a sx lock and *performs* an unbound sleep, so
there is a mismatch.

Btw, it sounds like allproc_lock and other similar locks are just
using an sx lock for *legacy*, they should be probabilly converted to
rwlock.
It also imposes little problems in the TTY layer, for example, where I
saw you need to use a unbounded sleeping primitive because of
processes locks acquisitions.

A nice janitor task would be to convert these sx locks into rw and see
what happens.

Thanks,
Attilio


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