Messages in this thread Patch in this message | | | Date | Wed, 4 Nov 2015 17:57:24 -0800 | From | "Paul E. McKenney" <> | Subject | Re: perf related lockdep bug |
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On Wed, Nov 04, 2015 at 03:34:19PM +0100, Peter Zijlstra wrote: > On Wed, Nov 04, 2015 at 06:01:33AM -0800, Paul E. McKenney wrote: > > On Wed, Nov 04, 2015 at 11:28:00AM +0100, Peter Zijlstra wrote: > > > On Wed, Nov 04, 2015 at 11:21:51AM +0100, Peter Zijlstra wrote: > > > > > > > The problem appears to be due to the new RCU expedited grace period > > > > stuff, with rcu_read_unlock() now randomly trying to acquire locks it > > > > previously didn't. > > > > > > > > Lemme go look at those rcu bits again.. > > > > > > Paul, I think this is because of: > > > > > > 8203d6d0ee78 ("rcu: Use single-stage IPI algorithm for RCU expedited grace period") > > > > > > What happens is that the IPI comes in and tags any random > > > rcu_read_unlock() with the special bit, which then goes on and takes > > > locks. > > > > > > Now the problem is that we have scheduler activity inside this lock; > > > the one reported lockdep seems easy enough to fix, see below. > > > > > > I'll got and see if there's more sites than can cause this. > > > > This one only happens during boot time, but it would be good hygiene > > in any case. May I have your SOB on this? > > Of course, > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Thank you, applied as shown below.
Thanx, Paul
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commit 05faf451f1239a28fcd63bf4b66c0db57d7b13f9 Author: Peter Zijlstra <peterz@infradead.org> Date: Wed Nov 4 08:22:05 2015 -0800
rcu: Move wakeup out from under rnp->lock This patch removes a potential deadlock hazard by moving the wake_up_process() in rcu_spawn_gp_kthread() out from under rnp->lock. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index caf3651fa5c9..183445959d00 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4323,8 +4323,8 @@ static int __init rcu_spawn_gp_kthread(void) sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); } - wake_up_process(t); raw_spin_unlock_irqrestore(&rnp->lock, flags); + wake_up_process(t); } rcu_spawn_nocb_kthreads(); rcu_spawn_boost_kthreads();
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