tools: Fix runqslower invalid read error when option -t was selected

tools/runqslower.py

@@ -114,16 +114,16 @@
 // calculate latency
 int trace_run(struct pt_regs *ctx, struct task_struct *prev)
 {
- u32 pid, tgid, prev_pid;
+ u32 pid, tgid;
 
  // ivcsw: treat like an enqueue event and store timestamp
- prev_pid = prev->pid;
  if (prev->STATE_FIELD == TASK_RUNNING) {
  tgid = prev->tgid;
+ pid = prev->pid;
  u64 ts = bpf_ktime_get_ns();
- if (prev_pid != 0) {
+ if (pid != 0) {
  if (!(FILTER_PID) && !(FILTER_TGID)) {
- start.update(&prev_pid, &ts);
+ start.update(&pid, &ts);
  }
  }
  }
@@ -144,7 +144,7 @@
 
  struct data_t data = {};
  data.pid = pid;
- data.prev_pid = prev_pid;
+ data.prev_pid = prev->pid;
  data.delta_us = delta_us;
  bpf_get_current_comm(&data.task, sizeof(data.task));
  bpf_probe_read_kernel_str(&data.prev_task, sizeof(data.prev_task), prev->comm);
@@ -181,27 +181,29 @@
  // TP_PROTO(bool preempt, struct task_struct *prev, struct task_struct *next)
  struct task_struct *prev = (struct task_struct *)ctx->args[1];
  struct task_struct *next= (struct task_struct *)ctx->args[2];
- u32 tgid, pid, prev_pid;
+ u32 tgid, pid;
  long state;
 
  // ivcsw: treat like an enqueue event and store timestamp
  bpf_probe_read_kernel(&state, sizeof(long), (const void *)&prev->STATE_FIELD);
- bpf_probe_read_kernel(&prev_pid, sizeof(prev->pid), &prev->pid);
+ bpf_probe_read_kernel(&pid, sizeof(prev->pid), &prev->pid);
  if (state == TASK_RUNNING) {
  bpf_probe_read_kernel(&tgid, sizeof(prev->tgid), &prev->tgid);
  u64 ts = bpf_ktime_get_ns();
- if (prev_pid != 0) {
+ if (pid != 0) {
  if (!(FILTER_PID) && !(FILTER_TGID)) {
- start.update(&prev_pid, &ts);
+ start.update(&pid, &ts);
  }
  }
 
  }
 
- bpf_probe_read_kernel(&pid, sizeof(next->pid), &next->pid);
-
+ u32 prev_pid;
  u64 *tsp, delta_us;
 
+ prev_pid = pid;
+ bpf_probe_read_kernel(&pid, sizeof(next->pid), &next->pid);
+
  // fetch timestamp and calculate delta
  tsp = start.lookup(&pid);
  if (tsp == 0) {