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### Description
This PR resolves a deadlock between AddressSanitizer (ASan) and
LeakSanitizer (LSan)
that occurs when both sanitizers attempt to acquire locks in conflicting
orders across
threads. The fix ensures safe lock acquisition ordering by preloading
module information
before error reporting.
---
### Issue Details
**Reproducer**
```cpp
// Thread 1: ASan error path
int arr[1] = {0};
std::thread t([&]() {
arr[1] = 1; // Triggers ASan OOB error
});
// Thread 2: LSan check path
__lsan_do_leak_check();
```
**Lock Order Conflict**:
- Thread 1 (ASan error reporting):
1. Acquires ASan thread registry lock (B)
1. Attempts to acquire libdl lock (A) via `dl_iterate_phdr`
- Thread 2 (LSan leak check):
1. Acquires libdl lock (A) via `dl_iterate_phdr`
1. Attempts to acquire ASan thread registry lock (B)
This creates a circular wait condition (A -> B -> A) meeting all four
Coffman deadlock criteria.
---
### Fix Strategy
The root cause lies in ASan's error reporting path needing
`dl_iterate_phdr` (requiring lock A)
while already holding its thread registry lock (B). The solution:
1. **Preload Modules Early**: Force module list initialization _before_
acquiring ASan's thread lock
2. **Avoid Nested Locking**: Ensure symbolization (via dl_iterate_phdr)
completes before error reporting locks
Key code change:
```cpp
// Before acquiring ASan's thread registry lock:
Symbolizer::GetOrInit()->GetRefreshedListOfModules();
```
This guarantees module information is cached before lock acquisition,
eliminating
the need for `dl_iterate_phdr` calls during error reporting.
---
### Testing
Added **asan_lsan_deadlock.cpp** test case:
- Reproduces deadlock reliably without fix **under idle system
conditions**
- Uses watchdog thread to detect hangs
- Verifies ASan error reports correctly without deadlock
**Note**: Due to the inherent non-determinism of thread scheduling and
lock acquisition timing,
this test may not reliably reproduce the deadlock on busy systems (e.g.,
during parallel
`ninja check-asan` runs).
---
### Impact
- Fixes rare but severe deadlocks in mixed ASan+LSan environments
- Maintains thread safety guarantees for both sanitizers
- No user-visible behavior changes except deadlock elimination
---
### Relevant Buggy Code
- Code in ASan's asan_report.cpp
```cpp
explicit ScopedInErrorReport(bool fatal = false)
: halt_on_error_(fatal || flags()->halt_on_error) {
// Acquire lock B
asanThreadRegistry().Lock();
}
~ScopedInErrorReport() {
...
// Try to acquire lock A under holding lock B via the following path
// #4 0x000071a353d83e93 in __GI___dl_iterate_phdr (
// callback=0x5d1a07a39580 <__sanitizer::dl_iterate_phdr_cb(dl_phdr_info*, unsigned long, void*)>,
// data=0x6da3510fd3f0) at ./elf/dl-iteratephdr.c:39
// #5 0x00005d1a07a39574 in __sanitizer::ListOfModules::init (this=0x71a353ebc080)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:784
// #6 0x00005d1a07a429e3 in __sanitizer::Symbolizer::RefreshModules (this=0x71a353ebc058)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_libcdep.cpp:188
// #7 __sanitizer::Symbolizer::FindModuleForAddress (this=this@entry=0x71a353ebc058,
// address=address@entry=102366378805727)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_libcdep.cpp:214
// #8 0x00005d1a07a4291b in __sanitizer::Symbolizer::SymbolizePC (this=0x71a353ebc058, addr=102366378805727)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_libcdep.cpp:88
// #9 0x00005d1a07a40df7 in __sanitizer::(anonymous namespace)::StackTraceTextPrinter::ProcessAddressFrames (
// this=this@entry=0x6da3510fd520, pc=102366378805727)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cpp:37
// #10 0x00005d1a07a40d27 in __sanitizer::StackTrace::PrintTo (this=this@entry=0x6da3510fd5e8,
// output=output@entry=0x6da3510fd588)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cpp:110
// #11 0x00005d1a07a410a1 in __sanitizer::StackTrace::Print (this=0x6da3510fd5e8)
// at llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cpp:133
// #12 0x00005d1a0798758d in __asan::ErrorGeneric::Print (
// this=0x5d1a07aa4e08 <__asan::ScopedInErrorReport::current_error_+8>)
// at llvm-project/compiler-rt/lib/asan/asan_errors.cpp:617
current_error_.Print();
...
}
```
- Code in LSan's lsan_common_linux.cpp
```cpp
void LockStuffAndStopTheWorld(StopTheWorldCallback callback,
CheckForLeaksParam *argument) {
// Acquire lock A
dl_iterate_phdr(LockStuffAndStopTheWorldCallback, ¶m);
}
static int LockStuffAndStopTheWorldCallback(struct dl_phdr_info *info,
size_t size, void *data) {
// Try to acquire lock B under holding lock A via the following path
// #3 0x000055555562b34a in __sanitizer::ThreadRegistry::Lock (this=<optimized out>)
// at llvm-project/compiler-rt/lib/asan/../sanitizer_common/sanitizer_thread_registry.h:99
// #4 __lsan::LockThreads () at llvm-project/compiler-rt/lib/asan/asan_thread.cpp:484
// #5 0x0000555555652629 in __lsan::ScopedStopTheWorldLock::ScopedStopTheWorldLock (this=<optimized out>)
// at llvm-project/compiler-rt/lib/lsan/lsan_common.h:164
// #6 __lsan::LockStuffAndStopTheWorldCallback (info=<optimized out>, size=<optimized out>, data=0x0,
// data@entry=0x7fffffffd158) at llvm-project/compiler-rt/lib/lsan/lsan_common_linux.cpp:120
ScopedStopTheWorldLock lock;
DoStopTheWorldParam *param = reinterpret_cast<DoStopTheWorldParam *>(data);
StopTheWorld(param->callback, param->argument);
return 1;
}
```
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