Re: [PATCH] OsdSynch.c modernization

John Baldwin wrote:
> 2007/9/22, Jung-uk Kim <jkim_at_freebsd.org>:
>> I thought exactly the same when I started rewriting it (almost half
>> year ago!).  I have tried all of the above, spent numerous sleepless
>> nights, and miserably failed. :-(
>>
>> Spin mutex is too restrictive (e.g., it cannot be used with other
>> locks gracefully).  critical_enter() causes:
>>
>> panic: blockable sleep lock (sleep mutex) 32 _at_
>> /usr/src/sys/vm/uma_core.c:1830 cpuid = 0
>> KDB: enter: panic
>> [thread pid 21 tid 100013 ]
>> Stopped at      kdb_enter+0x32: leave
> 
> However, disabling interrupts while you block on other locks is just as bad, 
> we just don't assert for it.  Better would be to fix ACPI-CA to not try to 
> malloc() while holding a spin lock.  You should be able to see where it is 
> doing that via the stack trace.  If the malloc is using M_NOWAIT you will be 
> far better off using a plain mutex and just not disabling interrupts.

For 7.0, we're going with what we have (sx locks) since it's well-tested
and not wrong, maybe just less than optimal.  Remember that acpi locks
are acquired a few dozen times every 10 seconds or so, so this is not at
risk of being a performance issue.

I think it's a good idea to work with Bob Moore to improve things on
their side as well.  Then we can revisit this and clean it up.

-- 
Nate