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[LLDB] Fix deadlock in module callback when running in parallel (#168425)

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When the target is being created, the target list acquires the mutex for
the duration of the target creation process. However if a module
callback is enabled and is being called in parallel there exists an
opportunity to deadlock if the callback calls into targetlist. I've
created a minimum repro
[here](https://gist.github.com/Jlalond/2557e06fa09825f338eca08b1d21884f).

```
command script import dead-lock-example (from above gist)
...
target create a.out
[hangs]
```

This looks like a straight forward fix, where `CreateTargetInternal`
doesn't access any state directly, and instead calls methods which they
themselves are thread-safe. So I've moved the lock to when we update the
list with the created target. I'm not sure if this is a comprehensive
fix, but it does fix my above example and in my (albeit limited)
testing, doesn't cause any strange change in behavior.
This commit is contained in:
Jacob Lalonde
2025-12-03 10:29:18 -08:00
committed by GitHub
parent a8ccd42ab2
commit 106edbdabe
2 changed files with 8 additions and 2 deletions
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5
lldb/include/lldb/Target/TargetList.h
View File

@@ -216,6 +216,11 @@ private:
llvm::StringRef triple_str, LoadDependentFiles load_dependent_files,
const OptionGroupPlatform *platform_options, lldb::TargetSP &target_sp);
// Create Target Internal does not modify any state directly, and should not
// be called under the target list mutex. Instead any state changes should
// call into methods which themselves are protected by the target list mutex.
// We need to do this so the locate module call back doesn't cause a re-entry
// dead lock when creating the target.
static Status CreateTargetInternal(Debugger &debugger,
llvm::StringRef user_exe_path,
const ArchSpec &arch,

5
lldb/source/Target/TargetList.cpp
View File

@@ -48,7 +48,7 @@ Status TargetList::CreateTarget(Debugger &debugger,
LoadDependentFiles load_dependent_files,
const OptionGroupPlatform *platform_options,
TargetSP &target_sp) {
std::lock_guard<std::recursive_mutex> guard(m_target_list_mutex);
auto result = TargetList::CreateTargetInternal(
debugger, user_exe_path, triple_str, load_dependent_files,
platform_options, target_sp);
@@ -63,7 +63,7 @@ Status TargetList::CreateTarget(Debugger &debugger,
const ArchSpec &specified_arch,
LoadDependentFiles load_dependent_files,
PlatformSP &platform_sp, TargetSP &target_sp) {
std::lock_guard<std::recursive_mutex> guard(m_target_list_mutex);
auto result = TargetList::CreateTargetInternal(
debugger, user_exe_path, specified_arch, load_dependent_files,
platform_sp, target_sp);
@@ -521,6 +521,7 @@ uint32_t TargetList::GetIndexOfTarget(lldb::TargetSP target_sp) const {
}
void TargetList::AddTargetInternal(TargetSP target_sp, bool do_select) {
std::lock_guard<std::recursive_mutex> guard(m_target_list_mutex);
lldbassert(!llvm::is_contained(m_target_list, target_sp) &&
"target already exists it the list");
UnregisterInProcessTarget(target_sp);