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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Stress concurrent SCX_KICK_WAIT calls to reproduce wait-cycle deadlock.
*
* Three CPUs are designated from userspace. Every enqueue from one of the
* three CPUs kicks the next CPU in the ring with SCX_KICK_WAIT, creating a
* persistent A -> B -> C -> A wait cycle pressure.
*/
#include <scx/common.bpf.h>
char _license[] SEC("license") = "GPL";
const volatile s32 test_cpu_a;
const volatile s32 test_cpu_b;
const volatile s32 test_cpu_c;
u64 nr_enqueues;
u64 nr_wait_kicks;
UEI_DEFINE(uei);
static s32 target_cpu(s32 cpu)
{
if (cpu == test_cpu_a)
return test_cpu_b;
if (cpu == test_cpu_b)
return test_cpu_c;
if (cpu == test_cpu_c)
return test_cpu_a;
return -1;
}
void BPF_STRUCT_OPS(cyclic_kick_wait_enqueue, struct task_struct *p,
u64 enq_flags)
{
s32 this_cpu = bpf_get_smp_processor_id();
s32 tgt;
__sync_fetch_and_add(&nr_enqueues, 1);
if (p->flags & PF_KTHREAD) {
scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_INF,
enq_flags | SCX_ENQ_PREEMPT);
return;
}
scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
tgt = target_cpu(this_cpu);
if (tgt < 0 || tgt == this_cpu)
return;
__sync_fetch_and_add(&nr_wait_kicks, 1);
scx_bpf_kick_cpu(tgt, SCX_KICK_WAIT);
}
void BPF_STRUCT_OPS(cyclic_kick_wait_exit, struct scx_exit_info *ei)
{
UEI_RECORD(uei, ei);
}
SEC(".struct_ops.link")
struct sched_ext_ops cyclic_kick_wait_ops = {
.enqueue = cyclic_kick_wait_enqueue,
.exit = cyclic_kick_wait_exit,
.name = "cyclic_kick_wait",
.timeout_ms = 1000U,
};
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