Messages in this thread | | | Date | Thu, 6 Sep 2012 15:08:21 -0700 | From | "Paul E. McKenney" <> | Subject | Re: lockdep WARNING on check_critical_timing() |
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On Thu, Sep 06, 2012 at 05:56:39PM -0400, Steven Rostedt wrote: > On Thu, 2012-09-06 at 14:29 -0700, Paul E. McKenney wrote: > > > > > Didn't we talk about having the rcu_dereference_raw() not do the check? > > > The function tracer is just too invasive to add work arounds to prevent > > > lockdep from screaming about it. > > > > Actually, rcu_dereference_raw() is already supposed to bypass the > > lockdep checks. And the code looks to me like it does the bypass, > > OR-ing "1" into the asssertion condition. > > > > So what am I missing here? > > >From my tree, I see: > > #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) > > #define rcu_dereference_check(p, c) \ > __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) > > Note the 'c' comes after rcu_read_lock_held() > > static inline int rcu_read_lock_held(void) > { > if (!debug_lockdep_rcu_enabled()) > return 1; > if (rcu_is_cpu_idle()) > return 0; > if (!rcu_lockdep_current_cpu_online()) > return 0; > return lock_is_held(&rcu_lock_map); > } > > Then when lock_is_held() is called, we get the false warning message.
OK, I can easily do:
__rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
But I am still missing why the order matters. Are you saying that lock_is_held() itself is doing the splat?
Thanx, Paul
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