tree b773010a88be3beeb4dfaf2658b76b40b448e98a
parent 52942b6b16c6ebb25f4dd4df0208d840ba0cbc5c
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1231129806 -0800
committer Ingo Molnar <mingo@elte.hu> 1231146628 +0100

rcu: fix rcutree grace-period-latency bug on small systems

Impact: fix delays during bootup

Kudos to Andi Kleen for finding a grace-period-latency problem!  The
problem was that the special-case code for small machines never updated
the ->signaled field to indicate that grace-period initialization had
completed, which prevented force_quiescent_state() from ever expediting
grace periods.  This problem resulted in grace periods extending for more
than 20 seconds.  Not subtle.  I introduced this bug during my inspection
process when I fixed a race between grace-period initialization and
force_quiescent_state() execution.

The following patch properly updates the ->signaled field for the
"small"-system case (no more than 32 CPUs for 32-bit kernels and no more
than 64 CPUs for 64-bit kernels).

Reported-by: Andi Kleen <andi@firstfloor.org>
Tested-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>