From f838fa820f9271008617c345c477122d9e29a05c Mon Sep 17 00:00:00 2001 From: jeffreytan81 Date: Mon, 5 Aug 2024 17:26:39 -0700 Subject: 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 --- .../Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp | 2 ++ 1 file changed, 2 insertions(+) (limited to 'lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp') diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp index 08d5f50..a0b08a2 100644 --- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp +++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp @@ -714,6 +714,8 @@ static const char *GetStopReasonString(StopReason stop_reason) { return "vfork"; case eStopReasonVForkDone: return "vforkdone"; + case eStopReasonInterrupt: + return "async interrupt"; case eStopReasonInstrumentation: case eStopReasonInvalid: case eStopReasonPlanComplete: -- cgit v1.1