From f535a607c13c7b674e0788ca5765779aa74a01c3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 22 Nov 2011 20:43:02 -0800 Subject: rcu: Eliminate RCU_FAST_NO_HZ grace-period hang With the new implementation of RCU_FAST_NO_HZ, it was possible to hang RCU grace periods as follows: o CPU 0 attempts to go idle, cycles several times through the rcu_prepare_for_idle() loop, then goes dyntick-idle when RCU needs nothing more from it, while still having at least on RCU callback pending. o CPU 1 goes idle with no callbacks. Both CPUs can then stay in dyntick-idle mode indefinitely, preventing the RCU grace period from ever completing, possibly hanging the system. This commit therefore prevents CPUs that have RCU callbacks from entering dyntick-idle mode. This approach also eliminates the need for the end-of-grace-period IPIs used previously. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/trace/events/rcu.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include/trace') diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index debe453c..8dd6fcb 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -287,7 +287,6 @@ TRACE_EVENT(rcu_dyntick, * * "No callbacks": Nothing to do, no callbacks on this CPU. * "In holdoff": Nothing to do, holding off after unsuccessful attempt. - * "Dyntick with callbacks": Callbacks remain, but RCU doesn't need CPU. * "Begin holdoff": Attempt failed, don't retry until next jiffy. * "More callbacks": Still more callbacks, try again to clear them out. * "Callbacks drained": All callbacks processed, off to dyntick idle! -- cgit v1.1