fjricci created this revision.
fjricci added reviewers: jingham, clayborg, andrew.w.kaylor.
fjricci added subscribers: lldb-commits, sas.
The gdb-remote async thread cannot modify thread state while the main thread
holds a lock on the state. Don't use locking thread iteration for bt all.
Specifically, the deadlock manifests when lldb attempts to JIT code to
symbolicate objective c while backtracing. As part of this code path,
SetPrivateState() is called on an async thread. This async thread will
block waiting for the thread_list lock held by the main thread in
CommandObjectIterateOverThreads. The main thread will also block on the
async thread during DoResume (although with a timeout), leading to a
deadlock. Due to the timeout, the deadlock is not immediately apparent,
but the inferior will be left in an invalid state after the bt all completes,
and objective-c symbols will not be successfully resolved in the backtrace.
http://reviews.llvm.org/D18075
Files:
source/Commands/CommandObjectThread.cpp
Index: source/Commands/CommandObjectThread.cpp
===================================================================
--- source/Commands/CommandObjectThread.cpp
+++ source/Commands/CommandObjectThread.cpp
@@ -73,8 +73,13 @@
{
Process *process = m_exe_ctx.GetProcessPtr();
uint32_t idx = 0;
- for (ThreadSP thread_sp : process->Threads())
+
+ // Manually iterate to avoid locking the threadlist,
+ // which can cause deadlocks when JIT-ing code
+ ThreadList thread_list = process->GetThreadList();
+ for (uint32_t i = 0; i < thread_list.GetSize(); ++i)
{
+ ThreadSP thread_sp = thread_list.GetThreadAtIndex(i);
if (idx != 0 && m_add_return)
result.AppendMessage("");
Index: source/Commands/CommandObjectThread.cpp
===================================================================
--- source/Commands/CommandObjectThread.cpp
+++ source/Commands/CommandObjectThread.cpp
@@ -73,8 +73,13 @@
{
Process *process = m_exe_ctx.GetProcessPtr();
uint32_t idx = 0;
- for (ThreadSP thread_sp : process->Threads())
+
+ // Manually iterate to avoid locking the threadlist,
+ // which can cause deadlocks when JIT-ing code
+ ThreadList thread_list = process->GetThreadList();
+ for (uint32_t i = 0; i < thread_list.GetSize(); ++i)
{
+ ThreadSP thread_sp = thread_list.GetThreadAtIndex(i);
if (idx != 0 && m_add_return)
result.AppendMessage("");
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