On Mon, Oct 22, 2018 at 05:24:07PM +0200, Oleg Nesterov wrote:
> On 10/22, Paul E. McKenney wrote:
> >
> > The sync.c file has a number of calls to BUG_ON(), which panics the
> > kernel, which is not a good
>
> Agreed.
>
> I added these BUG_ON's for documentation when I was prototyping this code,
> perhaps we can simply remove them.
I do like this approach. ;-)
> > @@ -125,12 +125,12 @@ void rcu_sync_enter(struct rcu_sync *rsp)
> > rsp->gp_state = GP_PENDING;
> > spin_unlock_irq(&rsp->rss_lock);
> >
> > - BUG_ON(need_wait && need_sync);
> > -
> > if (need_sync) {
> > gp_ops[rsp->gp_type].sync();
> > rsp->gp_state = GP_PASSED;
> > wake_up_all(&rsp->gp_wait);
> > + if (WARN_ON_ONCE(need_wait))
> > + wait_event(rsp->gp_wait, rsp->gp_state == GP_PASSED);
>
> This wait_event(gp_state == GP_PASSED) is pointless, note that this branch
> does gp_state = GP_PASSED 2 lines above.
OK, I have removed this one.
> And if we add WARN_ON_ONCE(need_wait), then we should probably also add
> WARN_ON_ONCE(need_sync) into the next "if (need_wait)" branch just for
> symmetry.
But in that case, the earlier "if" prevents "need_sync" from ever getting
there, unless I lost the thread here.
> So I'd suggest to either turn that BUG_ON(need_wait && need_sync) above
> into WARN_ON_ONCE(wait && sync) or simply remove it.
I chose WARN_ON_ONCE() for this one.
> Again, the only purpose of this BUG_ON() is to explain to the reader that
> it is not (must not be) possible that, say, gp_state == GP_IDLE while
> gp_count != 0.
Good point!
Should I remove the others?
> ----------------------------------------------------------------------------
> Damn.
>
> This suddenly reminds me that I rewrote this code completely, and you even
> reviewed the new implementation and (iirc) acked it!
>
> However, I failed to force myself to rewrite the comments, and that is why
> I didn't send the "official" patch :/
>
> May be some time...
Could you please point me at the last email thread? Yes, I should be
able to find it, but I would probably get the wrong one. :-/
Thanx, Paul
