Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 24 Aug 2011 12:16:21 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH 2/6] x86, nmi: create new NMI handler routines |
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On Wed, Aug 24, 2011 at 08:19:54PM +0200, Peter Zijlstra wrote: > On Wed, 2011-08-24 at 14:16 -0400, Don Zickus wrote: > > On Wed, Aug 24, 2011 at 07:51:00PM +0200, Peter Zijlstra wrote: > > > On Wed, 2011-08-24 at 13:44 -0400, Don Zickus wrote: > > > > > > + rcu_read_lock(); > > > > > > + a = rcu_dereference_raw(*ap); > > > > > > > > > > The reason for rcu_dereference_raw() is to prevent lockdep from choking > > > > > due to being called from an NMI handler, correct? If so, please add a > > > > > comment to this effect on this and similar uses. > > > > > > > > That sounds right. But honestly, I just copied what notifier_call_chain > > > > had. Regardless, I will make sure to document that in my next version. > > > > Thanks! > > > > > > Not quite right, nmi_enter() does lockdep_disable() and makes > > > lock_is_held() return always true. > > > > > > I think this (and the other sites) could do with rcu_dereference_check(, > > > lockdep_is_held(&desc->lock)); not that it wouldn't be anything but > > > documentation since the actual test isn't working from NMI context but I > > > do think its worth it for that alone. > > > > So you want me to remove the _raw part of the dereference? I can test > > that with lockdep enabled to verify things don't go splat. > > Ah, right, its never used from the desc->lock context and we always hold > rcu_read_lock(), so a simple rcu_dereference() should indeed suffice.
Even better! ;-)
Thanx, Paul
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