[all-commits] [llvm/llvm-project] f838fa: New ThreadPlanSingleThreadTimeout to resolve poten...

[jeffreytan81 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f838fa820f9271008617c345c477122d9e29a05c
      https://github.com/llvm/llvm-project/commit/f838fa820f9271008617c345c477122d9e29a05c
  Author: jeffreytan81 <jeffreytan at meta.com>
  Date:   2024-08-05 (Mon, 05 Aug 2024)

  Changed paths:
    M lldb/include/lldb/Target/Process.h
    M lldb/include/lldb/Target/StopInfo.h
    M lldb/include/lldb/Target/Thread.h
    M lldb/include/lldb/Target/ThreadPlan.h
    A lldb/include/lldb/Target/ThreadPlanSingleThreadTimeout.h
    M lldb/include/lldb/Target/ThreadPlanStepOut.h
    M lldb/include/lldb/Target/ThreadPlanStepOverRange.h
    M lldb/include/lldb/Target/ThreadPlanStepRange.h
    A lldb/include/lldb/Target/TimeoutResumeAll.h
    M lldb/include/lldb/lldb-enumerations.h
    M lldb/source/API/SBThread.cpp
    M lldb/source/Interpreter/CommandInterpreter.cpp
    M lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp
    M lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
    M lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
    M lldb/source/Target/CMakeLists.txt
    M lldb/source/Target/Process.cpp
    M lldb/source/Target/StopInfo.cpp
    M lldb/source/Target/TargetProperties.td
    M lldb/source/Target/Thread.cpp
    M lldb/source/Target/ThreadPlan.cpp
    A lldb/source/Target/ThreadPlanSingleThreadTimeout.cpp
    M lldb/source/Target/ThreadPlanStepInRange.cpp
    M lldb/source/Target/ThreadPlanStepOverRange.cpp
    M lldb/source/Target/ThreadPlanStepRange.cpp
    A lldb/test/API/functionalities/single-thread-step/Makefile
    A lldb/test/API/functionalities/single-thread-step/TestSingleThreadStepTimeout.py
    A lldb/test/API/functionalities/single-thread-step/main.cpp
    M lldb/tools/lldb-dap/JSONUtils.cpp
    M lldb/tools/lldb-dap/LLDBUtils.cpp

  Log Message:
  -----------
  New ThreadPlanSingleThreadTimeout to resolve potential deadlock in single thread stepping (#90930)

This PR introduces a new `ThreadPlanSingleThreadTimeout` that will be
used to address potential deadlock during single-thread stepping.

While debugging a target with a non-trivial number of threads (around
5000 threads in one example target), we noticed that a simple step over
can take as long as 10 seconds. Enabling single-thread stepping mode
significantly reduces the stepping time to around 3 seconds. However,
this can introduce deadlock if we try to step over a method that depends
on other threads to release a lock.

To address this issue, we introduce a new
`ThreadPlanSingleThreadTimeout` that can be controlled by the
`target.process.thread.single-thread-plan-timeout` setting during
single-thread stepping mode. The concept involves counting the elapsed
time since the last internal stop to detect overall stepping progress.
Once a timeout occurs, we assume the target is not making progress due
to a potential deadlock, as mentioned above. We then send a new async
interrupt, resume all threads, and `ThreadPlanSingleThreadTimeout`
completes its task.

To support this design, the major changes made in this PR are:
1. `ThreadPlanSingleThreadTimeout` is popped during every internal stop
and reset (re-pushed) to the top of the stack (as a leaf node) during
resume. This is achieved by always returning `true` from
`ThreadPlanSingleThreadTimeout::DoPlanExplainsStop()` and
`ThreadPlanSingleThreadTimeout::MischiefManaged()`.
2. A new thread-specific async interrupt stop is introduced, which can
be detected/consumed by `ThreadPlanSingleThreadTimeout`.
3. The clearing of branch breakpoints in the range thread plan has been
moved from `DoPlanExplainsStop()` to `ShouldStop()`, as it is not
guaranteed that it will be called.

The detailed design is discussed in the RFC below:

[https://discourse.llvm.org/t/improve-single-thread-stepping/74599](https://discourse.llvm.org/t/improve-single-thread-stepping/74599)

---------

Co-authored-by: jeffreytan81 <jeffreytan at fb.com>



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