Re: [PATCH] OsdSynch.c modernization

On Monday 24 September 2007 12:11:07 pm Nate Lawson wrote:
> 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.

Disabling interrupts and then calling malloc() is wrong however.

-- 
John Baldwin