5.2.1-RC hangs occasionally when sound files are played using the pcm driver

[Don Lewis]

On 23 Feb, Brian O'Shea wrote:
> --- Brian O'Shea <b_oshea at yahoo.com> wrote:
>> --- Mathew Kanner <mat at cnd.mcgill.ca> wrote:
>> > 
>> > 	Hello Brian,
>> > 	Don Lewis commited changes to the 5.2- tree on 2/14.  Could
>> > you update and try again, also please do run with witness and
>> > invariants, and if possible try to get a crashdump so we can see
>> > what's happening.
>> 
>> Sure.  I'll try to reproduce it with witness and invariants first, just
>> to avoid changing too many conditions at the same time.  Failing that,
>> I'll update to the latest 5.2 tree and see if the problem goes away.
> 
> makeoptions     DEBUG=-g                #Build kernel with gdb(1) debug symbols
> options         INVARIANTS              #Enable calls of extra sanity checking
> options         INVARIANT_SUPPORT       #Extra sanity checks of internal
> structures, required by INVARIANTS
> options         WITNESS                 #Enable checks to detect deadlocks and
> cycles
> #options        WITNESS_SKIPSPIN        #Don't run witness on spinlocks for
> speed
> 
> Ok, the problem seems to happen much more reliably now, but still no
> panic (so no crash dump).  However, I did notice that for some reason
> I had built an SMP kernel.  All kernels that I have seen exhibit this pcm
> driver hang were apparently SMP kernels...I guess that's the default
> in GENERIC, which I copied and adapted for my kernel config.  As my system
> only has one CPU, I will build a UP kernel and see if that has any
> effect.

Witness won't trigger a panic.  It just prints some information to the
console about the error.

SMP is now the default and runs fine on UP boxes.