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sched_ext: Introduce scx_bpf_cpu_curr()

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Provide scx_bpf_cpu_curr() as a way for scx schedulers to check the curr
task of a remote rq without assuming its lock is held.

Many scx schedulers make use of scx_bpf_cpu_rq() to check a remote curr
(e.g. to see if it should be preempted). This is problematic because
scx_bpf_cpu_rq() provides access to all fields of struct rq, most of
which aren't safe to use without holding the associated rq lock.

Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Christian Loehle
2025-09-03 22:23:10 +01:00
committed by Tejun Heo
parent e0ca169638
commit 20b158094a
2 changed files with 15 additions and 0 deletions
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14
kernel/sched/ext.c
View File

@@ -6379,6 +6379,19 @@ __bpf_kfunc struct rq *scx_bpf_locked_rq(void)
return rq;
}
/**
* scx_bpf_cpu_curr - Return remote CPU's curr task
* @cpu: CPU of interest
*
* Callers must hold RCU read lock (KF_RCU).
*/
__bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu)
{
if (!kf_cpu_valid(cpu, NULL))
return NULL;
return rcu_dereference(cpu_rq(cpu)->curr);
}
/**
* scx_bpf_task_cgroup - Return the sched cgroup of a task
* @p: task of interest
@@ -6544,6 +6557,7 @@ BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_cpu_rq)
BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL)
BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU)
#ifdef CONFIG_CGROUP_SCHED
BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_RCU | KF_ACQUIRE)
#endif

1
tools/sched_ext/include/scx/common.bpf.h
View File

@@ -104,6 +104,7 @@ bool scx_bpf_task_running(const struct task_struct *p) __ksym;
s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym;
struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym;
struct rq *scx_bpf_locked_rq(void) __ksym;
struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym;
struct cgroup *scx_bpf_task_cgroup(struct task_struct *p) __ksym __weak;
u64 scx_bpf_now(void) __ksym __weak;
void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) __ksym __weak;