[all-commits] [llvm/llvm-project] 1db68f: tsan: fix mmap atomicity

[Dmitry Vyukov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1db68fcd8e76dc6437f028c8ace408aa7d04e647
      https://github.com/llvm/llvm-project/commit/1db68fcd8e76dc6437f028c8ace408aa7d04e647
  Author: Dmitry Vyukov <dvyukov at google.com>
  Date:   2021-06-24 (Thu, 24 Jun 2021)

  Changed paths:
    M compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
    A compiler-rt/test/tsan/mmap_stress2.cpp

  Log Message:
  -----------
  tsan: fix mmap atomicity

Mmap interceptor is not atomic in the sense that it
exposes unmapped shadow for a brief period of time.
This breaks programs that mmap over another mmap
and access the region concurrently.
Don't unmap shadow in the mmap interceptor to fix this.
Just mapping new shadow on top should be enough to zero it.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D104593