[tip: sched/core] sched/core: Fix context analysis errors in non-preferred CPU push

[tip-bot2 for Shrikanth Hegde]

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

Commit-ID:     4b1f75be23c4fb0016a102d1cb108ba355c4c00d
Gitweb:        https://git.kernel.org/tip/4b1f75be23c4fb0016a102d1cb108ba355c4c00d
Author:        Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
AuthorDate:    Tue, 29 Sep 2026 22:17:12 +05:30
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 01 Oct 2026 14:00:34 +02:00

sched/core: Fix context analysis errors in non-preferred CPU push

Nathan reported build failure with clang23 when CONFIG_PREFERRED_CPU=y.

  kernel/sched/core.c:11298:3: error: releasing raw_spinlock 'rq_lockp(rq)' that was not held [-Werror,-Wthread-safety-analysis]
   11298 |                 rq_unlock(rq, &rf);
         |                 ^
  kernel/sched/core.c:11303:1: error: raw_spinlock 'rq_lockp(__this_rq())' is not held on every path through here [-Werror,-Wthread-safety-analysis]

context_unsafe_alias(rq) was placed after rq_lock(), by which point it had
already associated the lock with the original rq alias.

Move the alias barrier before rq_lock() so that the changing rq alias is
accounted for before acquiring the lock.

Fixes: 74699f56ebcf ("sched/core: Push current task from non preferred CPU")
Closes: https://lore.kernel.org/all/20260929121838.GA1814129@ax162/
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> # build
Link: https://patch.msgid.link/20260929164712.1054883-1-sshegde@xxxxxxxxxxxxx
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0bb86a4..23677d7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11283,10 +11283,10 @@ static int sched_non_preferred_cpu_push_stop(void *arg)
 		 * safely bail out.
 		 */
 		cpu = select_fallback_rq(rq->cpu, p);
+		context_unsafe_alias(rq);
 		rq_lock(rq, &rf);
 		rq->npc_push_work_pending = false;
 		update_rq_clock(rq);
-		context_unsafe_alias(rq);
 
 		if (task_rq(p) == rq && task_on_rq_queued(p)) {
 			struct rq *dest_rq = __migrate_task(rq, &rf, p, cpu);