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sched_ext: idle: Validate locking correctness in scx_bpf_select_cpu_and()

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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>
This commit is contained in:
Andrea Righi 2025-05-15 21:11:43 +02:00 committed by Tejun Heo
parent 617a77018f
commit 686d133723
1 changed files with 10 additions and 0 deletions
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10
kernel/sched/ext_idle.c
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@ -935,6 +935,7 @@ __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 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