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rcu: Add ACCESS_ONCE() to ->qlen accesses 

The _rcu_barrier() function accesses other CPUs' rcu_data structure's
->qlen field without benefit of locking.  This commit therefore adds
the required ACCESS_ONCE() wrappers around accesses and updates that
need it.

ACCESS_ONCE() is not needed when a CPU accesses its own ->qlen, or
in code that cannot run while _rcu_barrier() is sampling ->qlen fields.

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 2012-05-09 15:44:42 -07:00 committed by Paul E. McKenney
parent 3f5d3ea64f
commit 1d1fb395f6
1 changed files with 4 additions and 4 deletions
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8
kernel/rcutree.c
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@ -1350,7 +1350,7 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
rsp->qlen += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
ACCESS_ONCE(rdp->qlen) = 0;
}
/*
@ -1600,7 +1600,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
}
smp_mb(); /* List handling before counting for rcu_barrier(). */
rdp->qlen_lazy -= count_lazy;
rdp->qlen -= count;
ACCESS_ONCE(rdp->qlen) -= count;
rdp->n_cbs_invoked += count;
/* Reinstate batch limit if we have worked down the excess. */
@ -1889,7 +1889,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
rdp->qlen++;
ACCESS_ONCE(rdp->qlen)++;
if (lazy)
rdp->qlen_lazy++;
else
@ -2423,7 +2423,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
init_callback_list(rdp);
rdp->qlen_lazy = 0;
rdp->qlen = 0;
ACCESS_ONCE(rdp->qlen) = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);