This issue looks similar to Bug ID - 747664. So marking the issue as Won't Fix.
Please re-open if not the case.
Thank You.

Testcase 5022828230606848 is a top crash on ClusterFuzz for linux platform. Please prioritize fixing this crash.

Marking this crash as a stable release blocker. If this is incorrect, remove the ReleaseBlock label.

ClusterFuzz has detected this issue as fixed in range 502656:502679.

Detailed report: https://clusterfuzz.com/testcase?key=5022828230606848

Fuzzer: tokenfuzz_pdf_march16
Job Type: linux_tsan_chrome_mp
Platform Id: linux

Crash Type: Data race ATOMIC READ 1
Crash Address: 0x7b0c00061f20
Crash State:
  pthread_mutex_lock
  pa_mutex_lock
  pa_xmalloc
  
Sanitizer: thread (TSAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_tsan_chrome_mp&range=471564:471571
Fixed: https://clusterfuzz.com/revisions?job=linux_tsan_chrome_mp&range=502656:502679

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5022828230606848

Additional requirements: Requires Gestures

See https://github.com/google/clusterfuzz-tools for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.