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rcu-tasks: Handle the running-offline idle-task special case

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The idle task corresponding to an offline CPU can appear to be running
while that CPU is offline.  This commit therefore adds checks for this
situation, treating it as a quiescent state.  Because the tasklist scan
and the holdout-list scan now exclude CPU-hotplug operations, readers
on the CPU-hotplug paths are still waited for.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-03-22 11:24:58 -07:00
parent 81b4a7bc3b
commit 7e3b70e070
1 changed files with 6 additions and 2 deletions
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8
kernel/rcu/tasks.h
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@ -818,16 +818,20 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
{
int cpu = task_cpu(t);
bool in_qs = false;
bool ofl = cpu_is_offline(cpu);
if (task_curr(t)) {
WARN_ON_ONCE(ofl & !is_idle_task(t));
// If no chance of heavyweight readers, do it the hard way.
if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
return false;
// If heavyweight readers are enabled on the remote task,
// we can inspect its state despite its currently running.
// However, we cannot safely change its state.
if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
if (!ofl && // Check for "running" idle tasks on offline CPUs.
!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
return false; // No quiescent state, do it the hard way.
in_qs = true;
} else {