diff options
| -rw-r--r-- | src/memory_region_map.cc | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/src/memory_region_map.cc b/src/memory_region_map.cc index 21cb377..05ba3bf 100644 --- a/src/memory_region_map.cc +++ b/src/memory_region_map.cc @@ -582,11 +582,31 @@ void MemoryRegionMap::RecordRegionAddition(const void* start, size_t size) { Region region; region.Create(start, size); // First get the call stack info into the local varible 'region': - const int depth = - max_stack_depth_ > 0 - ? MallocHook::GetCallerStackTrace(const_cast<void**>(region.call_stack), - max_stack_depth_, kStripFrames + 1) - : 0; + int depth = 0; + // NOTE: libunwind also does mmap and very much likely while holding + // it's own lock(s). So some threads may first take libunwind lock, + // and then take region map lock (necessary to record mmap done from + // inside libunwind). On the other hand other thread(s) may do + // normal mmap. Which would call this method to record it. Which + // would then proceed with installing that record to region map + // while holding region map lock. That may cause mmap from our own + // internal allocators, so attempt to unwind in this case may cause + // reverse order of taking libuwind and region map locks. Which is + // obvious deadlock. + // + // Thankfully, we can easily detect if we're holding region map lock + // and avoid recording backtrace in this (rare and largely + // irrelevant) case. By doing this we "declare" that thread needing + // both locks must take region map lock last. In other words we do + // not allow taking libuwind lock when we already have region map + // lock. Note, this is generally impossible when somebody tries to + // mix cpu profiling and heap checking/profiling, because cpu + // profiler grabs backtraces at arbitrary places. But at least such + // combination is rarer and less relevant. + if (max_stack_depth_ > 0 && !LockIsHeld()) { + depth = MallocHook::GetCallerStackTrace(const_cast<void**>(region.call_stack), + max_stack_depth_, kStripFrames + 1); + } region.set_call_stack_depth(depth); // record stack info fully RAW_VLOG(10, "New global region %p..%p from %p", reinterpret_cast<void*>(region.start_addr), |