1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * Stress concurrent SCX_KICK_WAIT calls to reproduce wait-cycle deadlock. 4 * 5 * Three CPUs are designated from userspace. Every enqueue from one of the 6 * three CPUs kicks the next CPU in the ring with SCX_KICK_WAIT, creating a 7 * persistent A -> B -> C -> A wait cycle pressure. 8 */ 9 #include <scx/common.bpf.h> 10 11 char _license[] SEC("license") = "GPL"; 12 13 const volatile s32 test_cpu_a; 14 const volatile s32 test_cpu_b; 15 const volatile s32 test_cpu_c; 16 17 u64 nr_enqueues; 18 u64 nr_wait_kicks; 19 20 UEI_DEFINE(uei); 21 22 static s32 target_cpu(s32 cpu) 23 { 24 if (cpu == test_cpu_a) 25 return test_cpu_b; 26 if (cpu == test_cpu_b) 27 return test_cpu_c; 28 if (cpu == test_cpu_c) 29 return test_cpu_a; 30 return -1; 31 } 32 33 void BPF_STRUCT_OPS(cyclic_kick_wait_enqueue, struct task_struct *p, 34 u64 enq_flags) 35 { 36 s32 this_cpu = bpf_get_smp_processor_id(); 37 s32 tgt; 38 39 __sync_fetch_and_add(&nr_enqueues, 1); 40 41 if (p->flags & PF_KTHREAD) { 42 scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_INF, 43 enq_flags | SCX_ENQ_PREEMPT); 44 return; 45 } 46 47 scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags); 48 49 tgt = target_cpu(this_cpu); 50 if (tgt < 0 || tgt == this_cpu) 51 return; 52 53 __sync_fetch_and_add(&nr_wait_kicks, 1); 54 scx_bpf_kick_cpu(tgt, SCX_KICK_WAIT); 55 } 56 57 void BPF_STRUCT_OPS(cyclic_kick_wait_exit, struct scx_exit_info *ei) 58 { 59 UEI_RECORD(uei, ei); 60 } 61 62 SEC(".struct_ops.link") 63 struct sched_ext_ops cyclic_kick_wait_ops = { 64 .enqueue = cyclic_kick_wait_enqueue, 65 .exit = cyclic_kick_wait_exit, 66 .name = "cyclic_kick_wait", 67 .timeout_ms = 1000U, 68 }; 69