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

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

[Shrikanth Hegde]

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")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/all/20260929121838.GA1814129@ax162/
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
base commit: tip/sched/core
1fb28c664a19 ("virt/steal_governor: Enable the driver")

 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 0bb86a43a592..23677d76f9d2 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);
-- 
2.52.0

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

[Nathan Chancellor]

On Tue, Sep 29, 2026 at 10:17:12PM +0530, Shrikanth Hegde wrote:
> 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")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/all/20260929121838.GA1814129@ax162/
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>

Tested-by: Nathan Chancellor <nathan@kernel.org> # build

Thanks for the quick fix!

> ---
> base commit: tip/sched/core
> 1fb28c664a19 ("virt/steal_governor: Enable the driver")
> 
>  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 0bb86a43a592..23677d76f9d2 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);
> -- 
> 2.52.0
> 

-- 
Cheers,
Nathan