path: root/kernel/rcu
diff options
authorBoqun Feng <boqun.feng@gmail.com>2019-10-08 13:01:40 +0800
committerPaul E. McKenney <paulmck@kernel.org>2019-12-09 12:24:56 -0800
commit9f08cf088676c12a5b53bd5a29cf04f00c787b5d (patch)
tree41e8ee93dc186a569b07f6f0ee0472f174c1edf0 /kernel/rcu
parentrcu: Use *_ONCE() to protect lockless ->expmask accesses (diff)
rcu: Avoid modifying mask_ofl_ipi in sync_rcu_exp_select_node_cpus()
The "mask_ofl_ipi" is used to track which CPUs get IPIed, however in the IPI sending loop, "mask_ofl_ipi" along with another variable "mask_ofl_test" might also get modified to record which CPUs' quiesent states must be reported by the sync_rcu_exp_select_node_cpus() at the end of sync_rcu_exp_select_node_cpus(). This overlap of roles can be confusing, so this patch cleans things a little by using "mask_ofl_ipi" solely for determining which CPUs must be IPIed and "mask_ofl_test" for solely determining on behalf of which CPUs sync_rcu_exp_select_node_cpus() must report a quiscent state. Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Acked-by: Marco Elver <elver@google.com>
Diffstat (limited to 'kernel/rcu')
1 files changed, 6 insertions, 7 deletions
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 69c5aa64fcfd..6a6f328a5f52 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -387,10 +387,10 @@ retry_ipi:
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
- if (!ret) {
- mask_ofl_ipi &= ~mask;
+ /* The CPU will report the QS in response to the IPI. */
+ if (!ret)
- }
/* Failed, raced with CPU hotplug operation. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if ((rnp->qsmaskinitnext & mask) &&
@@ -401,13 +401,12 @@ retry_ipi:
goto retry_ipi;
- /* CPU really is offline, so we can ignore it. */
- if (!(rnp->expmask & mask))
- mask_ofl_ipi &= ~mask;
+ /* CPU really is offline, so we must report its QS. */
+ if (rnp->expmask & mask)
+ mask_ofl_test |= mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* Report quiescent states for those that went offline. */
- mask_ofl_test |= mask_ofl_ipi;
if (mask_ofl_test)
rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);