linux-kernel - [tip: sched/urgent] sched/core: Dequeue PSI signals for blocked tasks that are delayed

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Message-ID: <172874255961.1442.979470319617499321.tip-bot2@tip-bot2>
Date: Sat, 12 Oct 2024 14:15:59 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 K Prateek Nayak <kprateek.nayak@....com>,
 Johannes Weiner <hannes@...xchg.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched/core: Dequeue PSI signals for blocked tasks
 that are delayed

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     f5aaff7bfa11fb0b2ee6b8fd7bbc16cfceea2ad3
Gitweb:        https://git.kernel.org/tip/f5aaff7bfa11fb0b2ee6b8fd7bbc16cfceea2ad3
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 10 Oct 2024 08:28:36 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 11 Oct 2024 10:49:33 +02:00

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: 152e11f6df29 ("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: Peter Zijlstra (Intel) <peterz@...radead.org>
Not-yet-signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Johannes Weiner <hannes@...xchg.org>
Link: https://lore.kernel.org/lkml/20241004123506.GR18071@noisy.programming.kicks-ass.net/ [1]
---
 kernel/sched/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a860996..9e09140 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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 @@ picked:
 
 		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);