Patch "sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops_bypass()" has been added to the 6.12-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops_bypass()

to the 6.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched_ext-replace-rq_lock-to-raw_spin_rq_lock-in-scx.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit cd27aa29a0476bae712bb54202cc3e91f1d1ef8b
Author: Changwoo Min <changwoo@xxxxxxxxxx>
Date:   Thu Jan 9 00:08:06 2025 +0900

    sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops_bypass()
    
    [ Upstream commit 6268d5bc10354fc2ab8d44a0cd3b042d49a0417e ]
    
    scx_ops_bypass() iterates all CPUs to re-enqueue all the scx tasks.
    For each CPU, it acquires a lock using rq_lock() regardless of whether
    a CPU is offline or the CPU is currently running a task in a higher
    scheduler class (e.g., deadline). The rq_lock() is supposed to be used
    for online CPUs, and the use of rq_lock() may trigger an unnecessary
    warning in rq_pin_lock(). Therefore, replace rq_lock() to
    raw_spin_rq_lock() in scx_ops_bypass().
    
    Without this change, we observe the following warning:
    
    ===== START =====
    [    6.615205] rq->balance_callback && rq->balance_callback != &balance_push_callback
    [    6.615208] WARNING: CPU: 2 PID: 0 at kernel/sched/sched.h:1730 __schedule+0x1130/0x1c90
    =====  END  =====
    
    Fixes: 0e7ffff1b811 ("scx: Fix raciness in scx_ops_bypass()")
    Signed-off-by: Changwoo Min <changwoo@xxxxxxxxxx>
    Acked-by: Andrea Righi <arighi@xxxxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 40f915f893e2..81235942555a 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4348,10 +4348,9 @@ static void scx_ops_bypass(bool bypass)
 	 */
 	for_each_possible_cpu(cpu) {
 		struct rq *rq = cpu_rq(cpu);
-		struct rq_flags rf;
 		struct task_struct *p, *n;
 
-		rq_lock(rq, &rf);
+		raw_spin_rq_lock(rq);
 
 		if (bypass) {
 			WARN_ON_ONCE(rq->scx.flags & SCX_RQ_BYPASSING);
@@ -4367,7 +4366,7 @@ static void scx_ops_bypass(bool bypass)
 		 * sees scx_rq_bypassing() before moving tasks to SCX.
 		 */
 		if (!scx_enabled()) {
-			rq_unlock(rq, &rf);
+			raw_spin_rq_unlock(rq);
 			continue;
 		}
 
@@ -4387,10 +4386,11 @@ static void scx_ops_bypass(bool bypass)
 			sched_enq_and_set_task(&ctx);
 		}
 
-		rq_unlock(rq, &rf);
-
 		/* resched to restore ticks and idle state */
-		resched_cpu(cpu);
+		if (cpu_online(cpu) || cpu == smp_processor_id())
+			resched_curr(rq);
+
+		raw_spin_rq_unlock(rq);
 	}
 unlock:
 	raw_spin_unlock_irqrestore(&__scx_ops_bypass_lock, flags);