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authorPaul E. McKenney <paul.mckenney@linaro.org>2011-11-23 13:38:58 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-12-11 10:32:04 -0800
commitc92b131bdcf89bf79870f1631d07547241a98f6c (patch)
tree618f38e1f4e6f71e056b240613a89915730b03f9 /kernel
parent3ad0decf98d97b9039d8ed47cee287366b929cdf (diff)
rcu: Remove dynticks false positives and RCU failures
Assertions in rcu_init_percpu_data() unknowingly relied on outgoing CPUs being turned off before reaching the idle loop. Unfortunately, when running under kvm/qemu on x86, CPUs really can get to idle before begin shut off. These CPUs are then born in dyntick-idle mode from an RCU perspective, which results in splats in rcu_init_percpu_data() and in RCU wrongly ignoring those CPUs despite them being active. This in turn can cause RCU to end grace periods prematurely, potentially freeing up memory that the newly onlined CPUs were still using. This is most decidedly not what we need to see in an RCU implementation. This commit therefore replaces the assertions in rcu_init_percpu_data() with code that forces RCU's dyntick-idle view of newly onlined CPUs to match reality. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcutree.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 13fab4a9f9f..aab9ed504b1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2054,8 +2054,9 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
- WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
- WARN_ON_ONCE((atomic_read(&rdp->dynticks->dynticks) & 0x1) != 1);
+ rdp->dynticks->dynticks_nesting = DYNTICK_TASK_NESTING;
+ atomic_set(&rdp->dynticks->dynticks,
+ (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
/*