linux-kernel - [tip: sched/core] sched: Fix trace_sched_switch(.prev

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Message-ID: <174413914101.31282.6876925851363406689.tip-bot2@tip-bot2>
Date: Tue, 08 Apr 2025 19:05:41 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Gabriele Monaco <gmonaco@...hat.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Fix trace_sched_switch(.prev_state)

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

Commit-ID:     8feb053d53194382fcfb68231296fdc220497ea6
Gitweb:        https://git.kernel.org/tip/8feb053d53194382fcfb68231296fdc220497ea6
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 19 Mar 2025 22:23:23 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 08 Apr 2025 20:55:51 +02:00

sched: Fix trace_sched_switch(.prev_state)

Gabriele noted that in case of signal_pending_state(), the tracepoint
sees a stale task-state.

Fixes: fa2c3254d7cf ("sched/tracing: Don't re-read p->state when emitting sched_switch event")
Reported-by: Gabriele Monaco <gmonaco@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Valentin Schneider <vschneid@...hat.com>
---
 kernel/sched/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cfaca30..042c978 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6571,12 +6571,14 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  * Otherwise marks the task's __state as RUNNING
  */
 static bool try_to_block_task(struct rq *rq, struct task_struct *p,
-			      unsigned long task_state)
+			      unsigned long *task_state_p)
 {
+	unsigned long task_state = *task_state_p;
 	int flags = DEQUEUE_NOCLOCK;
 
 	if (signal_pending_state(task_state, p)) {
 		WRITE_ONCE(p->__state, TASK_RUNNING);
+		*task_state_p = TASK_RUNNING;
 		return false;
 	}
 
@@ -6713,7 +6715,7 @@ static void __sched notrace __schedule(int sched_mode)
 			goto picked;
 		}
 	} else if (!preempt && prev_state) {
-		try_to_block_task(rq, prev, prev_state);
+		try_to_block_task(rq, prev, &prev_state);
 		switch_count = &prev->nvcsw;
 	}