Fix thread-safety violation in Allocations Profiler: Create a new per…

…-thread backtrace buffer in ptls (JuliaLang#44116)

* Fix thread-safety violation in Allocations Profiler:

Re-use the shared `ptls->bt_data` buffer from the thread-local storage
for the buffer, to ensure that each thread has a separate buffer.

This buffer is shared with the exception throwing mechanism, but is safe
to share since julia exception throwing never interleaves with
allocations profiling.

* Approach two: Create a separate per-thread allocations backtrace buffer.

* Update src/gc-alloc-profiler.cpp

Co-authored-by: Jameson Nash <[email protected]>

* Update src/gc-alloc-profiler.cpp

Co-authored-by: Jameson Nash <[email protected]>

* fix type error (JuliaLang#44235)

* Update src/gc-alloc-profiler.cpp

Co-authored-by: Jameson Nash <[email protected]>
Co-authored-by: Pete Vilter <[email protected]>

src/gc-alloc-profiler.cpp

@@ -49,15 +49,24 @@ jl_combined_results g_combined_results; // Will live forever.
 // === stack stuff ===
 
 jl_raw_backtrace_t get_raw_backtrace() JL_NOTSAFEPOINT {
- // A single large buffer to record backtraces onto
- static jl_bt_element_t static_bt_data[JL_MAX_BT_SIZE];
+ // We first record the backtrace onto a MAX-sized buffer, so that we don't have to
+ // allocate the buffer until we know the size. To ensure thread-safety, we use a
+ // per-thread backtrace buffer.
+ jl_ptls_t ptls = jl_current_task->ptls;
+ jl_bt_element_t *shared_bt_data_buffer = ptls->profiling_bt_buffer;
+ if (shared_bt_data_buffer == NULL) {
+ size_t size = sizeof(jl_bt_element_t) * (JL_MAX_BT_SIZE + 1);
+ shared_bt_data_buffer = (jl_bt_element_t*) malloc_s(size);
+ ptls->profiling_bt_buffer = shared_bt_data_buffer;
+ }
 
- size_t bt_size = rec_backtrace(static_bt_data, JL_MAX_BT_SIZE, 2);
+ size_t bt_size = rec_backtrace(shared_bt_data_buffer, JL_MAX_BT_SIZE, 2);
 
  // Then we copy only the needed bytes out of the buffer into our profile.
  size_t bt_bytes = bt_size * sizeof(jl_bt_element_t);
- jl_bt_element_t *bt_data = (jl_bt_element_t*) malloc(bt_bytes);
- memcpy(bt_data, static_bt_data, bt_bytes);
+ jl_bt_element_t *bt_data = (jl_bt_element_t*) malloc_s(bt_bytes);
+ memcpy(bt_data, shared_bt_data_buffer, bt_bytes);
+
 
  return jl_raw_backtrace_t{
  bt_data,

src/julia_threads.h

@@ -246,6 +246,8 @@ typedef struct _jl_tls_states_t {
  // Temporary backtrace buffer. Scanned for gc roots when bt_size > 0.
  struct _jl_bt_element_t *bt_data; // JL_MAX_BT_SIZE + 1 elements long
  size_t bt_size; // Size for backtrace in transit in bt_data
+ // Temporary backtrace buffer used only for allocations profiler.
+ struct _jl_bt_element_t *profiling_bt_buffer;
  // Atomically set by the sender, reset by the handler.
  volatile _Atomic(sig_atomic_t) signal_request; // TODO: no actual reason for this to be _Atomic
  // Allow the sigint to be raised asynchronously