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rcu: Avoid modifying mask_ofl_ipi in sync_rcu_exp_select_node_cpus()

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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>
This commit is contained in:
Boqun Feng 2019-10-08 13:01:40 +08:00 committed by Paul E. McKenney
parent 15c7c972cd
commit 9f08cf0886
1 changed files with 6 additions and 7 deletions
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13
kernel/rcu/tree_exp.h
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@ -387,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
}
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
put_cpu();
if (!ret) {
mask_ofl_ipi &= ~mask;
/* The CPU will report the QS in response to the IPI. */
if (!ret)
continue;
}
/* Failed, raced with CPU hotplug operation. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if ((rnp->qsmaskinitnext & mask) &&
@ -401,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
schedule_timeout_uninterruptible(1);
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);
}