From: Andrea Righi <arighi@nvidia.com>
Date: Thu, 15 May 2025 19:11:43 +0000 (+0200)
Subject: sched_ext: idle: Validate locking correctness in scx_bpf_select_cpu_and()
X-Git-Tag: v6.16-rc1~153^2~6
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=686d1337237161833684d8554c6e3ea2d692bd41;p=thirdparty%2Flinux.git

sched_ext: idle: Validate locking correctness in scx_bpf_select_cpu_and()

Validate locking correctness when accessing p->nr_cpus_allowed and
p->cpus_ptr inside scx_bpf_select_cpu_and(): if the rq lock is held,
access is safe; otherwise, require that p->pi_lock is held.

This allows to catch potential unsafe calls to scx_bpf_select_cpu_and().

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index f0ebf8b5b908e..716863f1f8cee 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -935,6 +935,7 @@ prev_cpu:
 __bpf_kfunc s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 				       const struct cpumask *cpus_allowed, u64 flags)
 {
+	struct rq *rq;
 	s32 cpu;
 
 	if (!kf_cpu_valid(prev_cpu, NULL))
@@ -946,6 +947,15 @@ __bpf_kfunc s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64
 	if (!scx_kf_allowed(SCX_KF_SELECT_CPU | SCX_KF_ENQUEUE))
 		return -EPERM;
 
+	/*
+	 * Validate locking correctness to access p->cpus_ptr and
+	 * p->nr_cpus_allowed: if we're holding an rq lock, we're safe;
+	 * otherwise, assert that p->pi_lock is held.
+	 */
+	rq = scx_locked_rq();
+	if (!rq)
+		lockdep_assert_held(&p->pi_lock);
+
 #ifdef CONFIG_SMP
 	/*
 	 * This may also be called from ops.enqueue(), so we need to handle