Commit 897ba84d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Handle idle tasks for recently offlined CPUs 



This commit identifies idle tasks for recently offlined CPUs as residing
in a quiescent state.  This is safe only because CPU-hotplug operations
are excluded during these checks.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.org>
parent 5c9a9ca4

kernel/rcu/tasks.h

+7 −8
Original line number Diff line number Diff line
@@ -1318,27 +1318,26 @@ static int trc_inspect_reader(struct task_struct *t, void *bhp_in) 
	int nesting;

	bool ofl = cpu_is_offline(cpu);



	if (task_curr(t)) {

		WARN_ON_ONCE(ofl && !is_idle_task(t));



	if (task_curr(t) && !ofl) {

		// If no chance of heavyweight readers, do it the hard way.

		if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))

		if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))

			return -EINVAL;



		// 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.

		n_heavy_reader_attempts++;

		if (!ofl && // Check for "running" idle tasks on offline CPUs.

		    !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))

		// Check for "running" idle tasks on offline CPUs.

		if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))

			return -EINVAL; // No quiescent state, do it the hard way.

		n_heavy_reader_updates++;

		if (ofl)

			n_heavy_reader_ofl_updates++;

		nesting = 0;

	} else {

		// The task is not running, so C-language access is safe.

		nesting = t->trc_reader_nesting;

		WARN_ON_ONCE(ofl && task_curr(t) && !is_idle_task(t));

		if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl)

			n_heavy_reader_ofl_updates++;

	}



	// If not exiting a read-side critical section, mark as checked