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 f0ebf8b5b908e2a36c519717f29def23fbe3e878..716863f1f8cee0ad358b6dc6dcac5946eb853482 100644 (file)
--- 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