On 12/05, Davide Libenzi wrote:
>
> On Wed, 5 Dec 2007, Oleg Nesterov wrote:
>
> > do_signal_stop() counts all sub-thread and sets ->group_stop_count
> > accordingly.
> > Every thread should decrement ->group_stop_count and stop, the last one
> > should
> > notify the parent.
> >
> > However a sub-thread can exit before it notices the signal_pending(), or it
> > may
> > be somewhere in do_exit() already. In that case the group stop never
> > finishes
> > properly.
> >
> > Note: this is a minimal fix, we can add some optimizations later. Say we can
> > return quickly if thread_group_empty(). Also, we can move some signal
> > related
> > code from exit_notify() to exit_signals().
> >
> > Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
>
> Looks OK for me, even though we're doing more work on the exit path. OTOH
> I don't see a non-racy way of doing it w/out grabbing the lock. Did you
> try to bench how much this change costs?
Yes, you are right, this unconditional spin_lock() is not good, especially for
exit_group/exec.
But please look at the next patch I am sending, it removes the pessimization
almost completely.
The only difference: when there is no group exit in progress, we are doing
spin_lock_irq(siglock);
if (!signal_pending()) {
unlock and return
}
while the current code does
if (!signal_pending())
return;
spin_lock_irq(siglock);
...
It would be nice to measure the difference, but I can't invent the test-case.
I tested (just in case) 100000 fork+exit 's
perl -e 'fork ? wait : exit for 1 .. 100_000'
with and without the patch, and didn't notice any difference as expected.
> Acked-by: Davide Libenzi <[EMAIL PROTECTED]>
Thanks for looking at this!
Oleg.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
