[all-commits] [llvm/llvm-project] 35acc3: tsan: fix a race when assigning ThreadSignalContext

[Peter Ammon via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 35acc32b3e6535213d3ec651c9b7870cf74fe0ec
      https://github.com/llvm/llvm-project/commit/35acc32b3e6535213d3ec651c9b7870cf74fe0ec
  Author: Peter Ammon <corydoras at ridiculousfish.com>
  Date:   2023-01-10 (Tue, 10 Jan 2023)

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

  Log Message:
  -----------
  tsan: fix a race when assigning ThreadSignalContext

The SigCtx function lazily allocates a ThreadSignalContext, and stores it
in the ThreadState. This function may be called by various interceptors and
the signal handler itself.

If SigCtx itself is interrupted by a signal, then (prior to this fix) there
was a possibility of allocating two ThreadSignalContexts. This not only
leaks, it fails to deliver the signal to the program's signal handler, as
the recorded signal is overwritten by the new ThreadSignalContext.

Fix this by using a CAS to swap in the ThreadSignalContext, preventing the
race. Add a test for this case.

Reviewed By: dvyukov, melver

Differential Revision: https://reviews.llvm.org/D140582