Commit 20b15809 authored by Christian Loehle's avatar Christian Loehle Committed by Tejun Heo
Browse files

sched_ext: Introduce scx_bpf_cpu_curr() 



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: default avatarChristian Loehle <christian.loehle@arm.com>
Acked-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent e0ca1696

kernel/sched/ext.c

+14 −0
Original line number Diff line number Diff line
@@ -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

tools/sched_ext/include/scx/common.bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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;