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rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses

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The ->n_force_qs_lh field is accessed without the benefit of any
synchronization, so this commit adds the needed ACCESS_ONCE() wrappers.
Yes, increments to ->n_force_qs_lh can be lost, but contention should
be low and the field is strictly statistical in nature, so this is not
a problem.

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 2013-12-03 09:24:02 -08:00
parent 6d0abeca32
commit 3660c2813f
2 changed files with 3 additions and 3 deletions
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4
kernel/rcu/tree.c
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@ -2304,7 +2304,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
if (rnp_old != NULL) if (rnp_old != NULL)
raw_spin_unlock(&rnp_old->fqslock); raw_spin_unlock(&rnp_old->fqslock);
if (ret) { if (ret) {
rsp->n_force_qs_lh++; ACCESS_ONCE(rsp->n_force_qs_lh)++;
return; return;
} }
rnp_old = rnp; rnp_old = rnp;
@ -2316,7 +2316,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
smp_mb__after_unlock_lock(); smp_mb__after_unlock_lock();
raw_spin_unlock(&rnp_old->fqslock); raw_spin_unlock(&rnp_old->fqslock);
if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
rsp->n_force_qs_lh++; ACCESS_ONCE(rsp->n_force_qs_lh)++;
raw_spin_unlock_irqrestore(&rnp_old->lock, flags); raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
return; /* Someone beat us to it. */ return; /* Someone beat us to it. */
} }

2
kernel/rcu/tree_trace.c
View file

@ -273,7 +273,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n", seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
rsp->n_force_qs, rsp->n_force_qs_ngp, rsp->n_force_qs, rsp->n_force_qs_ngp,
rsp->n_force_qs - rsp->n_force_qs_ngp, rsp->n_force_qs - rsp->n_force_qs_ngp,
rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen); ACCESS_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) { for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
if (rnp->level != level) { if (rnp->level != level) {
seq_puts(m, "\n"); seq_puts(m, "\n");