Re: pfind() in ithread handler
- From: "Attilio Rao" <attilio@xxxxxxxxxxx>
- Date: Thu, 28 Feb 2008 15:04:55 +0100
2008/2/28, Yuri Pankov <yuri.pankov@xxxxxxxxx>:
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
--
Peace can only be achieved by understanding - A. Einstein
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