Messages in this thread | | | Date | Thu, 25 Aug 2011 14:40:45 -0700 | From | "Paul E. McKenney" <> | Subject | Re: 2.6.39.4: Oops in rcu_read_unlock_special()/_raw_spin_lock() |
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On Thu, Aug 25, 2011 at 02:28:19PM -0400, Will Simoneau wrote: > On 07:07 Thu 25 Aug , Paul E. McKenney wrote: > > On Thu, Aug 25, 2011 at 09:20:51AM -0400, Will Simoneau wrote: > > > On 14:27 Wed 24 Aug , Paul E. McKenney wrote: > > > > On Wed, Aug 24, 2011 at 05:19:07PM -0400, Will Simoneau wrote: > > > > > The following commits from Linus' git seem vaguely related, > > > > > although I have no idea how relevant they are to 2.6.39.4: > > > > > > > > > > ec433f0c (softirq,rcu: Inform RCU of irq_exit() activity) > > > > > 10f39bb1 (rcu: protect __rcu_read_unlock() against scheduler-using > > > > > irq handlers) > > > > > > > > If this failure mechanism really is the culprit, you should be able > > > > to make failure happen much more frequently by inserting a delay in > > > > __rcu_read_unlock() just prior to the call to rcu_read_unlock_special(). > > > > I would suggest starting with a few tens to hundreds of microseconds > > > > worth of delay. > > > > > > > > If this does make the failure reproducible, then it would make sense > > > > to try applying the two patches you identified. > > > > > > Hmm. I tried adding progressively larger delays in the spot you > > > indicated. I went from 100uS to an entire 1S (!) and got no crash or > > > deadlock. The target runs at 40MHz so the delays do need to be > > > relatively long compared to modern machines. > > > > > > My hardware breakpoint as well as printk tests confirm that > > > rcu_read_unlock_special() really does get called multiple times per > > > second, and the 1S delay makes it painfully obvious as well. But, no > > > dice. > > > > Well, you can always apply the two patches above anyway, but it is hard > > to prove what the underlying problem really is in your case. > > I am still unable to reproduce the Oops so I have no way of knowing if > applying the patches has any effect. I did find and fix the issue with > booting post-2.6.39* kernels on my hardware, so I've moved on to > 3.1-rc3. I guess I will get back to you if it happens again :-)
Fair enough! ;-)
Thanx, Paul
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