Hi,

On Sun, May 18, 2025 at 06:35:28AM -0400, Sasha Levin wrote:

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

sched_ext: Fix missing rq lock in scx_bpf_cpuperf_set()

to the 6.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: sched_ext-fix-missing-rq-lock-in-scx_bpf_cpuperf_set.patch and it can be found in the queue-6.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

This requires upstream commit 18853ba782bef ("sched_ext: Track currently locked rq").

Thanks, -Andrea

commit e0dd90f92931fd4040aee0bf75b348a402464821 Author: Andrea Righi arighi@nvidia.com Date: Tue Apr 22 10:26:33 2025 +0200

sched_ext: Fix missing rq lock in scx_bpf_cpuperf_set()

[ Upstream commit a11d6784d7316a6c77ca9f14fb1a698ebbb3c1fb ] scx_bpf_cpuperf_set() can be used to set a performance target level on any CPU. However, it doesn't correctly acquire the corresponding rq lock, which may lead to unsafe behavior and trigger the following warning, due to the lockdep_assert_rq_held() check: [ 51.713737] WARNING: CPU: 3 PID: 3899 at kernel/sched/sched.h:1512 scx_bpf_cpuperf_set+0x1a0/0x1e0 ... [ 51.713836] Call trace: [ 51.713837] scx_bpf_cpuperf_set+0x1a0/0x1e0 (P) [ 51.713839] bpf_prog_62d35beb9301601f_bpfland_init+0x168/0x440 [ 51.713841] bpf__sched_ext_ops_init+0x54/0x8c [ 51.713843] scx_ops_enable.constprop.0+0x2c0/0x10f0 [ 51.713845] bpf_scx_reg+0x18/0x30 [ 51.713847] bpf_struct_ops_link_create+0x154/0x1b0 [ 51.713849] __sys_bpf+0x1934/0x22a0 Fix by properly acquiring the rq lock when possible or raising an error if we try to operate on a CPU that is not the one currently locked. Fixes: d86adb4fc0655 ("sched_ext: Add cpuperf support") Signed-off-by: Andrea Righi arighi@nvidia.com Acked-by: Changwoo Min changwoo@igalia.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 77cdff0d9f348..0067f540a3f0f 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -7459,13 +7459,32 @@ __bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf) } if (ops_cpu_valid(cpu, NULL)) {

• struct rq *rq = cpu_rq(cpu);
  

• struct rq *rq = cpu_rq(cpu), *locked_rq = scx_locked_rq();
  

• struct rq_flags rf;
  

• /*
  

•  * When called with an rq lock held, restrict the operation
  

•  * to the corresponding CPU to prevent ABBA deadlocks.
  

•  */
  

• if (locked_rq && rq != locked_rq) {
  

• 	scx_ops_error("Invalid target CPU %d", cpu);
  

• 	return;
  

• }
  

• /*
  

•  * If no rq lock is held, allow to operate on any CPU by
  

•  * acquiring the corresponding rq lock.
  

•  */
  

• if (!locked_rq) {
  

• 	rq_lock_irqsave(rq, &rf);
  

• 	update_rq_clock(rq);
  

• }
  

rq->scx.cpuperf_target = perf;

• cpufreq_update_util(rq, 0);
  

• rcu_read_lock_sched_notrace();
  

• cpufreq_update_util(cpu_rq(cpu), 0);
  

• rcu_read_unlock_sched_notrace();
  

• if (!locked_rq)
  

• 	rq_unlock_irqrestore(rq, &rf);
  

  }

}