Commit f5aaff7b authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched/core: Dequeue PSI signals for blocked tasks that are delayed 

psi_dequeue() in for blocked task expects psi_sched_switch() to clear
the TSK_.*RUNNING PSI flags and set the TSK_IOWAIT flags however
psi_sched_switch() uses "!task_on_rq_queued(prev)" to detect if the task
is blocked or still runnable which is no longer true with DELAY_DEQUEUE
since a blocking task can be left queued on the runqueue.

This can lead to PSI splats similar to:

    psi: inconsistent task state! task=... cpu=... psi_flags=4 clear=0 set=4

when the task is requeued since the TSK_RUNNING flag was not cleared
when the task was blocked.

Explicitly communicate that the task was blocked to psi_sched_switch()
even if it was delayed and is still on the runqueue.

  [ prateek: Broke off the relevant part from [1], commit message ]

Fixes: 152e11f6 ("sched/fair: Implement delayed dequeue")
Closes: https://lore.kernel.org/lkml/20240830123458.3557-1-spasswolf@web.de/
Closes: https://lore.kernel.org/all/cd67fbcd-d659-4822-bb90-7e8fbb40a856@molgen.mpg.de/


Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Not-yet-signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/lkml/20241004123506.GR18071@noisy.programming.kicks-ass.net/ [1]
parent 98442f0c

kernel/sched/core.c

+3 −1
Original line number Diff line number Diff line
@@ -6537,6 +6537,7 @@ static void __sched notrace __schedule(int sched_mode) 
	 * as a preemption by schedule_debug() and RCU.

	 */

	bool preempt = sched_mode > SM_NONE;

	bool block = false;

	unsigned long *switch_count;

	unsigned long prev_state;

	struct rq_flags rf;
@@ -6622,6 +6623,7 @@ static void __sched notrace __schedule(int sched_mode) 
			 * After this, schedule() must not care about p->state any more.

			 */

			block_task(rq, prev, flags);

			block = true;

		}

		switch_count = &prev->nvcsw;

	}
@@ -6667,7 +6669,7 @@ static void __sched notrace __schedule(int sched_mode) 


		migrate_disable_switch(rq, prev);

		psi_account_irqtime(rq, prev, next);

		psi_sched_switch(prev, next, !task_on_rq_queued(prev));

		psi_sched_switch(prev, next, block);



		trace_sched_switch(preempt, prev, next, prev_state);