Commit-ID: c92b131bdcf89bf79870f1631d07547241a98f6c Gitweb: http://git.kernel.org/tip/c92b131bdcf89bf79870f1631d07547241a98f6c Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> AuthorDate: Wed, 23 Nov 2011 13:38:58 -0800 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Sun, 11 Dec 2011 10:32:04 -0800 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@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- kernel/rcutree.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 13fab4a..aab9ed5 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. */ /* -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|