On Thu, Jul 12, 2007 at 12:18:23PM +0300, Ranko Zivojnovic wrote:
> On Thu, 2007-07-12 at 09:37 +0200, Jarek Poplawski wrote:
> > On Wed, Jul 11, 2007 at 04:41:37PM +0300, Ranko Zivojnovic wrote:
> > > Signed-off-by: Ranko Zivojnovic <[EMAIL PROTECTED]>
> >
> > Maybe it's only my issue, but it seems there are no tabs: all spaces...
>
> Nope - you are right - just noticed my mailer converts tabs into spaces
> - sorry about this...
>
> >
> > ...plus some old doubts:
> >
>
> > - setup_timer(&elist[idx].timer, est_timer, est->interval);
> > + setup_timer(&elist[idx].timer, est_timer, idx);
> >
>
> I left this because setup_timer expects unsigned long.
Are there any warnings? It'll look strange without such comment.
I didn't check this, but maybe idx should be unsigned too?
>
> > ...
> > > /**
> > > * gen_kill_estimator - remove a rate estimator
> > > * @bstats: basic statistics
> > > @@ -195,31 +201,28 @@ int gen_new_estimator(struct gnet_stats_basic
> > > *bstats,
> > > *
> > > * Removes the rate estimator specified by &bstats and &rate_est
> > > * and deletes the timer.
> > > + *
> > > + * NOTE: Called under rtnl_mutex
> > > */
> > > void gen_kill_estimator(struct gnet_stats_basic *bstats,
> > > struct gnet_stats_rate_est *rate_est)
> > > {
> > ...
> > > + list_for_each_entry_safe(e, n, &elist[idx].list, list) {
> > > + if (e->rate_est != rate_est || e->bstats !=
> > > bstats)
> > > + continue;
> > >
> > > - kfree(est);
> > > - killed++;
> > > + list_del_rcu(&e->list);
> > > + call_rcu(&e->e_rcu, __gen_kill_estimator);
> > > }
> > > - if (killed && elist[idx].list == NULL)
> > > - del_timer(&elist[idx].timer);
> > > }
> > > }
> >
> > I've done a bit of mess last time, so maybe it was forgotten, but I
> > still think this kind of race is possible:
> >
> > - gen_kill_estimator is called during qdisc_destroy under
> > dev->queue_lock,
> > - est_timer is running and waiting on this lock just on the
> > list entry of the destroyed class,
> > - gen_kill_estimator kills the entry and returns,
> > - in xxx_destroy_class kfree(cl) is done etc.,
> > - est_timer gets the lock and does nbytes = e->bstats->bytes or
> > e->rate_est-bps = ... with freed memory.
...
> I don't mind fixing all the classful qdiscs to call_rcu() to release
> their class structures for consistency purposes ... in fact ... that is
> exactly what I will do in order to avoid any potential future mishaps.
> One may actually decide in the future to add a callback to a user
> defined function to update some qdisc/class specific rates and given
> this inconsistency in handling qdiscs vs classes - it could have a nasty
> backfire.
I don't know if such broad changes are acceptable, or if it's even
required that these structs have to belong to a class struct.
IMHO, unless I miss something, they could be included into
gen_estimator struct after some api change. BTW, maybe it would be
resonable to return a pointer to such gen_estimator from
gen_new_estimator, then lookups could be avoided in
gen_kill_estimator.
Alas, there is probably more (of course very unprobable): there
is no dev_hold for gen_estimator now, so I hope it'll always manage
to unlock in time - before dev is freed.
Jarek P.
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