kernel.git/kernel/sched/rt.c, branch linux-rolling-stable

sched/rt: Skip currently executing CPU in rto_next_cpu()

2026-02-26T23:00:49Z

[ Upstream commit 94894c9c477e53bcea052e075c53f89df3d2a33e ] CPU0 becomes overloaded when hosting a CPU-bound RT task, a non-CPU-bound RT task, and a CFS task stuck in kernel space. When other CPUs switch from RT to non-RT tasks, RT load balancing (LB) is triggered; with HAVE_RT_PUSH_IPI enabled, they send IPIs to CPU0 to drive the execution of rto_push_irq_work_func. During push_rt_task on CPU0, if next_task->prio < rq->donor->prio, resched_curr() sets NEED_RESCHED and after the push operation completes, CPU0 calls rto_next_cpu(). Since only CPU0 is overloaded in this scenario, rto_next_cpu() should ideally return -1 (no further IPI needed). However, multiple CPUs invoking tell_cpu_to_push() during LB increments rd->rto_loop_next. Even when rd->rto_cpu is set to -1, the mismatch between rd->rto_loop and rd->rto_loop_next forces rto_next_cpu() to restart its search from -1. With CPU0 remaining overloaded (satisfying rt_nr_migratory && rt_nr_total > 1), it gets reselected, causing CPU0 to queue irq_work to itself and send self-IPIs repeatedly. As long as CPU0 stays overloaded and other CPUs run pull_rt_tasks(), it falls into an infinite self-IPI loop, which triggers a CPU hardlockup due to continuous self-interrupts. The trigging scenario is as follows: cpu0 cpu1 cpu2 pull_rt_task tell_cpu_to_push <------------irq_work_queue_on rto_push_irq_work_func push_rt_task resched_curr(rq) pull_rt_task rto_next_cpu tell_cpu_to_push <-------------------------- atomic_inc(rto_loop_next) rd->rto_loop != next rto_next_cpu irq_work_queue_on rto_push_irq_work_func Fix redundant self-IPI by filtering the initiating CPU in rto_next_cpu(). This solution has been verified to effectively eliminate spurious self-IPIs and prevent CPU hardlockup scenarios. Fixes: 4bdced5c9a29 ("sched/rt: Simplify the IPI based RT balancing logic") Suggested-by: Steven Rostedt (Google) Suggested-by: K Prateek Nayak Signed-off-by: Chen Jinghuang Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (Google) Reviewed-by: Valentin Schneider Link: https://patch.msgid.link/20260122012533.673768-1-chenjinghuang2@huawei.com Signed-off-by: Sasha Levin

sched/proxy: Yield the donor task

2025-11-11T11:33:36Z

When executing a task in proxy context, handle yields as if they were requested by the donor task. This matches the traditional PI semantics of yield() as well. This avoids scenario like proxy task yielding, pick next task selecting the same previous blocked donor, running the proxy task again, etc. Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202510211205.1e0f5223-lkp@intel.com Suggested-by: Peter Zijlstra Signed-off-by: Fernand Sieber Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20251106104022.195157-1-sieberf@amazon.com

sched: Add support to pick functions to take rf

2025-10-16T09:13:55Z

Some pick functions like the internal pick_next_task_fair() already take rf but some others dont. We need this for scx's server pick function. Prepare for this by having pick functions accept it. [peterz: - added RETRY_TASK handling - removed pick_next_task_fair indirection] Signed-off-by: Joel Fernandes Signed-off-by: Peter Zijlstra (Intel) Acked-by: Tejun Heo

sched: Detect per-class runqueue changes

2025-10-16T09:13:55Z

Have enqueue/dequeue set a per-class bit in rq->queue_mask. This then enables easy tracking of which runqueues are modified over a lock-break. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Tejun Heo

sched: Move sched_class::prio_changed() into the change pattern

2025-10-16T09:13:52Z

Move sched_class::prio_changed() into the change pattern. And while there, extend it with sched_class::get_prio() in order to fix the deadline sitation. Suggested-by: Tejun Heo Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Juri Lelli Acked-by: Tejun Heo Acked-by: Vincent Guittot

sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern

2025-10-16T09:13:51Z

Add {DE,EN}QUEUE_CLASS and fold the sched_class::switch* methods into the change pattern. This completes and makes the pattern more symmetric. This changes the order of callbacks slightly: OLD NEW | | switching_from() dequeue_task(); | dequeue_task() put_prev_task(); | put_prev_task() | switched_from() | ... change task ... | ... change task ... | switching_to(); | switching_to() enqueue_task(); | enqueue_task() set_next_task(); | set_next_task() prev_class->switched_from() | switched_to() | switched_to() | Notably, it moves the switched_from() callback right after the dequeue/put. Existing implementations don't appear to be affected by this change in location -- specifically the task isn't enqueued on the class in question in either location. Make (CLASS)^(SAVE|MOVE), because there is nothing to save-restore when changing scheduling classes. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Juri Lelli Acked-by: Tejun Heo Acked-by: Vincent Guittot

sched: Fix proxy/current (push,pull)ability

2025-07-14T15:16:33Z

Proxy execution forms atomic pairs of tasks: The waiting donor task (scheduling context) and a proxy (execution context). The donor task, along with the rest of the blocked chain, follows the proxy wrt CPU placement. They can be the same task, in which case push/pull doesn't need any modification. When they are different, however, FIFO1 & FIFO42: ,-> RT42 | | blocked-on | v blocked_donor | mutex | | owner | v `-- RT1 RT1 RT42 CPU0 CPU1 ^ ^ | | overloaded !overloaded rq prio = 42 rq prio = 0 RT1 is eligible to be pushed to CPU1, but should that happen it will "carry" RT42 along. Clearly here neither RT1 nor RT42 must be seen as push/pullable. Unfortunately, only the donor task is usually dequeued from the rq, and the proxy'ed execution context (rq->curr) remains on the rq. This can cause RT1 to be selected for migration from logic like the rt pushable_list. Thus, adda a dequeue/enqueue cycle on the proxy task before __schedule returns, which allows the sched class logic to avoid adding the now current task to the pushable_list. Furthermore, tasks becoming blocked on a mutex don't need an explicit dequeue/enqueue cycle to be made (push/pull)able: they have to be running to block on a mutex, thus they will eventually hit put_prev_task(). Signed-off-by: Valentin Schneider Signed-off-by: Connor O'Brien Signed-off-by: John Stultz Signed-off-by: Peter Zijlstra (Intel) Tested-by: K Prateek Nayak Link: https://lkml.kernel.org/r/20250712033407.2383110-8-jstultz@google.com

sched/deadline: Fix accounting after global limits change

2025-07-14T08:59:33Z

A global limits change (sched_rt_handler() logic) currently leaves stale and/or incorrect values in variables related to accounting (e.g. extra_bw). Properly clean up per runqueue variables before implementing the change and rebuild scheduling domains (so that accounting is also properly restored) after such a change is complete. Reported-by: Marcel Ziswiler Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Tested-by: Marcel Ziswiler # nuc & rock5b Link: https://lore.kernel.org/r/20250627115118.438797-4-juri.lelli@redhat.com

sched/smp: Use the SMP version of the RT scheduling class

2025-06-13T06:47:20Z

Simplify the scheduler by making CONFIG_SMP=y primitives and data structures unconditional in the RT policies scheduler. Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Linus Torvalds Cc: Mel Gorman Cc: Sebastian Andrzej Siewior Cc: Shrikanth Hegde Cc: Steven Rostedt Cc: Valentin Schneider Cc: Vincent Guittot Link: https://lore.kernel.org/r/20250528080924.2273858-29-mingo@kernel.org

sched/smp: Make SMP unconditional

2025-06-13T06:47:18Z

Simplify the scheduler by making CONFIG_SMP=y primitives and data structures unconditional. Introduce transitory wrappers for functionality not yet converted to SMP. Note that this patch is pretty large, because there's no clear separation between various aspects of the SMP scheduler, it's basically a huge block of #ifdef CONFIG_SMP. A fair amount of it has to be switched on for it to boot and work on UP systems. Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Linus Torvalds Cc: Mel Gorman Cc: Sebastian Andrzej Siewior Cc: Shrikanth Hegde Cc: Steven Rostedt Cc: Valentin Schneider Cc: Vincent Guittot Link: https://lore.kernel.org/r/20250528080924.2273858-21-mingo@kernel.org