Refactor offcputime stack id error handling

tools/offcputime.py

@@ -35,6 +35,11 @@ def positive_nonzero_int(val):
  raise argparse.ArgumentTypeError("must be nonzero")
  return ival
 
+def stack_id_err(stack_id):
+ # -EFAULT in get_stackid normally means the stack-trace is not availible,
+ # Such as getting kernel stack trace in userspace code
+ return (stack_id < 0) and (stack_id != -errno.EFAULT)
+
 # arguments
 examples = """examples:
  ./offcputime # trace off-CPU stack time until Ctrl-C
@@ -199,9 +204,8 @@ def signal_ignore(signal, frame):
 bpf_text = bpf_text.replace('MAXBLOCK_US_VALUE', str(args.max_block_time))
 
 # handle stack args
-kernel_stack_get = "stack_traces.get_stackid(ctx, BPF_F_REUSE_STACKID)"
-user_stack_get = \
- "stack_traces.get_stackid(ctx, BPF_F_REUSE_STACKID | BPF_F_USER_STACK)"
+kernel_stack_get = "stack_traces.get_stackid(ctx, 0)"
+user_stack_get = "stack_traces.get_stackid(ctx, BPF_F_USER_STACK)"
 stack_context = ""
 if args.user_stacks_only:
  stack_context = "user"
@@ -260,16 +264,13 @@ def signal_ignore(signal, frame):
 counts = b.get_table("counts")
 stack_traces = b.get_table("stack_traces")
 for k, v in sorted(counts.items(), key=lambda counts: counts[1].value):
- # handle get_stackid erorrs
- if (not args.user_stacks_only and k.kernel_stack_id < 0) or \
- (not args.kernel_stacks_only and k.user_stack_id < 0 and
- k.user_stack_id != -errno.EFAULT):
+ # handle get_stackid errors
+ if not args.user_stacks_only and stack_id_err(k.kernel_stack_id):
+ missing_stacks += 1
+ has_enomem = has_enomem or k.kernel_stack_id == -errno.ENOMEM
+ if not args.kernel_stacks_only and stack_id_err(k.user_stack_id):
  missing_stacks += 1
- # check for an ENOMEM error
- if k.kernel_stack_id == -errno.ENOMEM or \
- k.user_stack_id == -errno.ENOMEM:
- has_enomem = True
- continue
+ has_enomem = has_enomem or k.user_stack_id == -errno.ENOMEM
 
  # user stacks will be symbolized by tgid, not pid, to avoid the overhead
  # of one symbol resolver per thread
@@ -282,25 +283,43 @@ def signal_ignore(signal, frame):
  # print folded stack output
  user_stack = list(user_stack)
  kernel_stack = list(kernel_stack)
- line = [k.name.decode()] + \
- [b.sym(addr, k.tgid) for addr in reversed(user_stack)] + \
- (need_delimiter and ["-"] or []) + \
- [b.ksym(addr) for addr in reversed(kernel_stack)]
+ line = [k.name.decode()]
+ # if we failed to get the stack is, such as due to no space (-ENOMEM) or
+ # hash collision (-EEXIST), we still print a placeholder for consistency
+ if not args.kernel_stacks_only:
+ if stack_id_err(k.user_stack_id):
+ line.append("[Missed User Stack]")
+ else:
+ line.extend([b.sym(addr, k.tgid) for addr in reversed(user_stack)])
+ if not args.user_stacks_only:
+ line.extend(["-"] if (need_delimiter and k.kernel_stack_id >= 0) else [])
+ if stack_id_err(k.kernel_stack_id):
+ line.append("[Missed Kernel Stack]")
+ else:
+ line.extend([b.ksym(addr) for addr in reversed(kernel_stack)])
  print("%s %d" % (";".join(line), v.value))
  else:
  # print default multi-line stack output
- for addr in kernel_stack:
- print(" %s" % b.ksym(addr))
- if need_delimiter:
- print(" --")
- for addr in user_stack:
- print(" %s" % b.sym(addr, k.tgid))
+ if not args.user_stacks_only:
+ if stack_id_err(k.kernel_stack_id):
+ print(" [Missed Kernel Stack]")
+ else:
+ for addr in kernel_stack:
+ print(" %s" % b.ksym(addr))
+ if not args.kernel_stacks_only:
+ if need_delimiter and k.user_stack_id >= 0:
+ print(" --")
+ if stack_id_err(k.user_stack_id):
+ print(" [Missed User Stack]")
+ else:
+ for addr in user_stack:
+ print(" %s" % b.sym(addr, k.tgid))
  print(" %-16s %s (%d)" % ("-", k.name.decode(), k.pid))
  print(" %d\n" % v.value)
 
 if missing_stacks > 0:
  enomem_str = "" if not has_enomem else \
  " Consider increasing --stack-storage-size."
- print("WARNING: %d stack traces could not be displayed.%s" %
+ print("WARNING: %d stack traces lost and could not be displayed.%s" %
  (missing_stacks, enomem_str),
  file=stderr)