Updated rusage patch

[Bruce Evans]

On Fri, 1 Jun 2007, Jeff Roberson wrote:

> On Fri, 1 Jun 2007, Bruce Evans wrote:

> Well, I think the whole exit/wait path could probably use some attention. 
> There is an incredible amount of locking and unlocking to deal with various 
> races and lock order issues.  And there are many subtle effects which aren't 
> immediately obvious.  I'm nervous about how many bugs might be caused if we 
> start going down this path so close to 7.0.

I'm afraid to look too closely :-).

>> Related bugs:
>> - td_[usip]ticks are still under (j) (sched_lock) in proc.h.
>> - td_(uu,us}ticks have always (?) been under (k) (thread-local).  That
>>  is more correct than (j), but they are updated by an interrupt handler
>>  and seem to be accessed without disabling interrupts elsewhere.
[See other replies for large modifications to this]

> Well td_[uisp]ticks are set and cleared while the sched_lock is held.  In 
> threadlock.diff the thread lock is responsible for this.  That reminds me 
> that I didn't add the per-thread locking to rufetch() in the patch I posted 
> earlier.

But the ticks fields aren't aren't under sched_lock in the patches or
committed version.  The could easily be under time_lock, but were
carefully pushed out of that too in the time_lock changes.  Per-thread
locking in statclock() and rufetch() could fix this but would give more
locking overhead in statclock().

Bruce