From: Paul E. McKenney <paul.mckenney@linaro.org>
Date: Wed, 23 Nov 2011 04:43:02 +0000 (-0800)
Subject: rcu: Eliminate RCU_FAST_NO_HZ grace-period hang
X-Git-Tag: v3.3-rc1~193^2^2~18
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f535a607c13c7b674e0788ca5765779aa74a01c3;p=pandora-kernel.git

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 <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

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