Messages in this thread | | | Date | Tue, 17 Mar 2015 17:56:21 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 tip/core/rcu 01/22] smpboot: Add common code for notification from dying CPU |
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On Tue, Mar 17, 2015 at 03:08:46PM +0100, Peter Zijlstra wrote: > On Tue, Mar 17, 2015 at 04:36:48AM -0700, Paul E. McKenney wrote: > > On Tue, Mar 17, 2015 at 09:18:07AM +0100, Peter Zijlstra wrote: > > > On Mon, Mar 16, 2015 at 11:37:45AM -0700, Paul E. McKenney wrote: > > > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > > > > > RCU ignores offlined CPUs, so they cannot safely run RCU read-side code. > > > > (They -can- use SRCU, but not RCU.) This means that any use of RCU > > > > during or after the call to arch_cpu_idle_dead(). Unfortunately, > > > > commit 2ed53c0d6cc99 added a complete() call, which will contain RCU > > > > read-side critical sections if there is a task waiting to be awakened. > > > > > > Got a little more detail there? > > > > Quite possibly. But exactly what sort of detail are you looking for? > > What exact RCU usage you ran into that was problematic. It seems to > imply that calling complete() -- from a dead cpu -- which ends up in > try_to_wake_up() was the problem?
Hmm, I'm thinking its select_task_rq_*(). And yes, 'fixing' this in the wake-up path will penalize everybody for the benefit of the very rare case someone is doing a hotplug.
So yeah, maybe this is the best solution.. Ulgy though :/
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