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Date: Tue, 13 Oct 2020 12:34:06 +0200 From: Peter Zijlstra <peterz@...radead.org> To: "Paul E. McKenney" <paulmck@...nel.org> Cc: Boqun Feng <boqun.feng@...il.com>, Qian Cai <cai@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>, linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org, Linux Next Mailing List <linux-next@...r.kernel.org>, Stephen Rothwell <sfr@...b.auug.org.au> Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion On Mon, Oct 12, 2020 at 02:28:12PM -0700, Paul E. McKenney wrote: > It is certainly an accident waiting to happen. Would something like > the following make sense? Sadly no. > ------------------------------------------------------------------------ > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index bfd38f2..52a63bc 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4067,6 +4067,7 @@ void rcu_cpu_starting(unsigned int cpu) > > rnp = rdp->mynode; > mask = rdp->grpmask; > + lockdep_off(); > raw_spin_lock_irqsave_rcu_node(rnp, flags); > WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); > newcpu = !(rnp->expmaskinitnext & mask); > @@ -4086,6 +4087,7 @@ void rcu_cpu_starting(unsigned int cpu) > } else { > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > + lockdep_on(); > smp_mb(); /* Ensure RCU read-side usage follows above initialization. */ > } This will just shut it up, but will not fix the actual problem of that spin-lock ending up in trace_lock_acquire() which relies on RCU which isn't looking. What we need here is to supress tracing not lockdep. Let me consider.
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