Commit ded467dc authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched, lockdep: Annotate ->pi_lock recursion 



There's a valid ->pi_lock recursion issue where the actual PI code
tries to wake up the stop task. Make lockdep aware so it doesn't
complain about this.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Reviewed-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lkml.kernel.org/r/20201023102347.406912197@infradead.org
parent 95158a89

kernel/sched/core.c

+15 −0
Original line number Diff line number Diff line
@@ -2658,6 +2658,7 @@ int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags) 


void sched_set_stop_task(int cpu, struct task_struct *stop)

{

	static struct lock_class_key stop_pi_lock;

	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };

	struct task_struct *old_stop = cpu_rq(cpu)->stop;
@@ -2673,6 +2674,20 @@ void sched_set_stop_task(int cpu, struct task_struct *stop) 
		sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);



		stop->sched_class = &stop_sched_class;



		/*

		 * The PI code calls rt_mutex_setprio() with ->pi_lock held to

		 * adjust the effective priority of a task. As a result,

		 * rt_mutex_setprio() can trigger (RT) balancing operations,

		 * which can then trigger wakeups of the stop thread to push

		 * around the current task.

		 *

		 * The stop task itself will never be part of the PI-chain, it

		 * never blocks, therefore that ->pi_lock recursion is safe.

		 * Tell lockdep about this by placing the stop->pi_lock in its

		 * own class.

		 */

		lockdep_set_class(&stop->pi_lock, &stop_pi_lock);

	}



	cpu_rq(cpu)->stop = stop;