Messages in this thread | | | Date | Mon, 11 Jul 2011 10:00:14 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 0/6] Check for use of RCU from dyntick-idle mode |
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On Mon, Jul 11, 2011 at 06:44:08PM +0200, Frederic Weisbecker wrote: > On Mon, Jul 11, 2011 at 09:38:48AM -0700, Paul E. McKenney wrote: > > On Mon, Jul 11, 2011 at 06:03:32PM +0200, Frederic Weisbecker wrote: > > > On Fri, Jul 08, 2011 at 08:43:31AM -0700, Paul E. McKenney wrote: > > > > Hello! > > > > > > > > This set of patches adds checks for use of RCU from "extended quiescent > > > > states" such as dyntick-idle mode. Such use is grossly illegal because > > > > RCU by definition ignores CPUs that are in extended quiescent states. > > > > In the case of dyntick-idle mode, the only way for RCU to avoid ignoring > > > > such CPUs would be to wake them up periodically, which would defeat the > > > > whole purpose of dyntick-idle mode. > > > > > > > > The good news is that Frederic got this effort started. The bad news is > > > > that there are several cases where RCU read-side critical sections appear > > > > in dyntick-idle mode. > > > > > > Ok, let me send to you the patch that splits up rcu/tickless logic and I'll try > > > to fix up what you reported to me in ppc. > > > > Very good, thank you! > > > > > BTW, are you aware of other cases? You mentioned "several" :) > > > > PowerPC's hypercall-exit trace event will also cause this complaint. > > Ok looking at this.
Oh, and I removed some of my RCU dyntick-idle trace events because they triggered this warning. This would of course be a problem regardless of where the RCU dyntick-idle APIs were called from, so I just took the approach of more carefully placing the trace events.
> > Plus I thought you saw some others. > > Nope, mine were spurious. In my v1 rcu_dereference_check warned if rcu read lock > wasn't held but didn't handle the rest of the conditional (another lock held or > simply 1 in rcu_dereference_raw()). > > In the v3, the one you applied, they legitimately disappeared.
OK, good to know!
Thanx, Paul
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