On Mon, Jun 21, 2010 at 11:02:37PM -0700, John Stultz wrote: > On Mon, 2010-06-21 at 16:55 +0200, Peter Zijlstra wrote: > > On Tue, 2010-06-22 at 00:48 +1000, Nick Piggin wrote: > > > > Right, so I was staring at the -rt splat, so its John who created that > > > > wreckage? > > > > > > It was, but apparently they saw an RCU bug there somewhere and hit it > > > with the big hammer. I haven't been able to reproduce it on a non-rt > > > kernel yet, and I see yet why RCU is not good enough here. > > > > John, could you describe the failure you spotted? > > The problem was that the rcu_read_lock() on the dentry ascending wasn't > preventing d_put/d_kill from removing entries from the parent node. So > the next entry we tried to follow was invalid. So we were getting odd > oopses from select_parent(). Oh, ah OK that makes sense. I was thinking it was a use after grace period problem. Hmm, I'll think about whether we can fix it better. > > I'm not as familiar with the rcu rules there, so the patch I made just > held the locks as it went down the chain. Not ideal of course, but still > an improvement over the dcache_lock that was there prior. > > Peter: I'm sorry, I've been out for a few days. Can you give me some > background on what brought this up and what -rt splat you mean? > > thanks > -john > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
