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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2009-01-04 20:30:06 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-01-05 10:10:28 +0100 |
| commit | c12172c0251761c54260376eb29a5f6547495580 (patch) | |
| tree | b773010a88be3beeb4dfaf2658b76b40b448e98a | |
| parent | 52942b6b16c6ebb25f4dd4df0208d840ba0cbc5c (diff) | |
| download | linux-c12172c0251761c54260376eb29a5f6547495580.tar.gz linux-c12172c0251761c54260376eb29a5f6547495580.tar.bz2 linux-c12172c0251761c54260376eb29a5f6547495580.zip | |
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>
| -rw-r--r-- | kernel/rcutree.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a342b032112c..88d921c5c449 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -572,6 +572,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { rnp->qsmask = rnp->qsmaskinit; + rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ spin_unlock_irqrestore(&rnp->lock, flags); return; } |