Messages in this thread | | | Date | Thu, 25 Aug 2011 07:07:22 -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 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 below Oops/BUGs were captured on a serial console during a large > > > rsync job. I do not know of a way to reproduce the Oops, I've only seen > > > it once. Some recent changes have been made suspiciously close to the > > > exploding code, which makes me think that maybe 2.6.39-stable is lacking > > > some fixes? 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.
Thanx, Paul
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