Messages in this thread | | | Date | Sat, 16 Jun 2007 03:59:12 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH -rt] Fix TASKLET_STATE_SCHED WARN_ON() |
| |
On 06/15, john stultz wrote: > > On Fri, 2007-06-15 at 19:52 +0400, Oleg Nesterov wrote: > > > > Could you please look at the message below? I sent it privately near a month > > ago, but I think these problems are not fixed yet. > > Hmm. Maybe you sent it to others on the cc list, as I can't find it in > my box. But apologies anyway.
checking my mbox... Oops, you are right, sorry!
> > > + if (unlikely(atomic_read(&t->count))) { > > > +out_disabled: > > > + /* implicit unlock: */ > > > + wmb(); > > > + t->state = TASKLET_STATEF_PENDING; > > > > What if tasklet_enable() happens just before this line ? > > > > After the next schedule_tasklet() we have all bits set: SCHED, RUN, PENDING. > > The next invocation of __tasklet_action() clears SCHED, but tasklet_tryunlock() > > below can never succeed because of PENDING. > > Yep. I've only been focusing on races in schedule/action, as I've been > hunting issues w/ rcu. But I'll agree that the other state changes look > problematic. I know Paul McKenney was looking at some of the other state > changes and was seeing some potential problems as well.
OK, thanks. But doesn't this mean your 2-nd patch is questionable?
> + } else { > + /* This is subtle. If we hit the corner case above > + * It is possible that we get preempted right here, > + * and another task has successfully called > + * tasklet_schedule(), then this function, and > + * failed on the trylock. Thus we must be sure > + * before releasing the tasklet lock, that the > + * SCHED_BIT is clear. Otherwise the tasklet > + * may get its SCHED_BIT set, but not added to the > + * list > + */ > + if (!tasklet_tryunlock(t)) > + goto again;
Again, tasklet_tryunlock() can fail because _PENDING was set by __tasklet_action(). In that case __tasklet_common_schedule() goes to the endless loop, no?
Oleg.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |