Messages in this thread | | | Date | Fri, 29 Jun 2012 16:01:52 -0700 | From | "Paul E. McKenney" <> | Subject | Re: rcu: BUG: spinlock recursion on CPU#3, trinity-child19/5970 |
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On Sat, Jun 30, 2012 at 12:40:07AM +0200, Sasha Levin wrote: > On Fri, 2012-06-29 at 15:27 -0700, Paul E. McKenney wrote: > > On Fri, Jun 29, 2012 at 11:40:40PM +0200, Sasha Levin wrote: > > > On Fri, 2012-06-29 at 10:23 -0700, Paul E. McKenney wrote: > > > > On Fri, Jun 29, 2012 at 12:09:44PM +0200, Sasha Levin wrote: > > > > > Hi Paul, > > > > > > > > > > I think I've stumbled on another bug that will increase your paranoia levels even further. > > > > > > > > > > I got the following lockup when fuzzing with trinity inside a KVM tools guest, using latest linux-next. > > > > > > > > > > It appears that it was caused by a03d6178 ("rcu: Move RCU grace-period cleanup into kthread"). This issue doesn't reproduce easily though, it took some fuzzing before hitting it. > > > > > > > > Hmmm... If the preemption at that point in __rcu_read_unlock() is > > > > required to make this happen, then it would be pretty hard to hit. > > > > I suspect that you can make it reproduce more quickly by putting > > > > a udelay(10) or similar right after the assignment of INT_MIN to > > > > t->rcu_read_lock_nesting in __rcu_read_unlock() in kernel/rcupdate.c. > > > > Can this be reproduced while running with lockdep enabled? > > > > > > The good news are that it is much easier to reproduce it by adding a udelay(10) at the point you've mentioned. > > > > How quickly does it reproduce? > > 10 seconds more or less.
Very good -- if an alleged fix survives for 10 minutes, we have excellent statistical confidence that it is in fact a fix.
Thanx, Paul
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