Deadlock while using stack tracer(ftrace)

Solution Verified - Updated -

Issue

  • When writing debugfs/tracing/stack_max_size while reading debugfs/tracing/stack_trace, we got deadlock. Because the 2 actions can be racy, and result in holding the same lock twice.

  • Step to Reproduce:

  1. echo 1 > /proc/sys/kernel/stack_tracer_enabled
  2. mount -t debugfs xxx /sys/kernel/debug
  3. for ((; ;)) ; do echo 1 > /sys/kernel/debug/tracing/stack_max_size; done
  4. for ((; ;)) ; do cat /sys/kernel/debug/tracing/stack_trace > /dev/null; done
  5. Then, wait for a while (until transparent hugepage is used.)
  6. move the task to /cgroup/A/
  7. rmdir /cgroup/A/B
  • Actual Results:
    • lockup
  • Expected Results:
    • Never lockup

Environment

  • Red Hat Enterprise Linux RHEL 6.0

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