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rcu: Disallow callback registry on offline CPUs

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Posting a callback after the CPU_DEAD notifier effectively leaks
that callback unless/until that CPU comes back online.  Silence is
unhelpful when attempting to track down such leaks, so this commit emits
a WARN_ON_ONCE() and unconditionally leaks the callback when an offline
CPU attempts to register a callback.  The rdp->nxttail[RCU_NEXT_TAIL] is
set to NULL in the CPU_DEAD notifier and restored in the CPU_UP_PREPARE
notifier, allowing _call_rcu() to determine exactly when posting callbacks
is illegal.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2012-08-03 13:16:15 -07:00 committed by Paul E. McKenney
parent 1331e7a1bb
commit 0d8ee37e2f
1 changed files with 10 additions and 0 deletions
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10
kernel/rcutree.c
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@ -1505,6 +1505,9 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
cpu, rdp->qlen, rdp->nxtlist);
init_callback_list(rdp);
/* Disallow further callbacks on this CPU. */
rdp->nxttail[RCU_NEXT_TAIL] = NULL;
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
@ -1927,6 +1930,12 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL)) {
/* _call_rcu() is illegal on offline CPU; leak the callback. */
WARN_ON_ONCE(1);
local_irq_restore(flags);
return;
}
ACCESS_ONCE(rdp->qlen)++;
if (lazy)
rdp->qlen_lazy++;
@ -2464,6 +2473,7 @@ 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;
init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
atomic_set(&rdp->dynticks->dynticks,
(atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);