Re: [PATCH] OsdSynch.c modernization

On Monday 24 September 2007 12:28 pm, John Baldwin wrote:
> 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.

Understood.  As I said earlier, I really like to fix it correctly.

<rant>
However, the problem is that there are so many different BIOSes out 
there, taking so different code paths.  Whenever I thought it's 
fixed, someone says 'you broke my laptop' or 'FreeBSD is bad because 
it doesn't boot on my laptop but Linux and Windows boot fine'. :-(
</rant>

(At least on my laptop) I found the malloc() was called from our code, 
i.e., AcpiOsExecute() from OsdSched.c.  I'll try something shortly 
cause I was going to rewrite the file anyway.

Thanks,

Jung-uk Kim