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[committed] libstdc++: Fix memory leak in PSTL TBB backend [PR117276]

Message ID 20250912131020.1974294-1-jwakely@redhat.com
State Committed
Commit d8f1655a781a76f5c86b3545b181b2005e585d29
Headers
Series [committed] libstdc++: Fix memory leak in PSTL TBB backend [PR117276] |

Commit Message

Jonathan Wakely Sept. 12, 2025, 1:10 p.m. UTC 
  Backport of upstream patch:
https://github.com/uxlfoundation/oneDPL/pull/1589

libstdc++-v3/ChangeLog:

	PR libstdc++/117276
	* include/pstl/parallel_backend_tbb.h (__func_task::finalize):
	Make deallocation unconditional.
---

Tested x86_64-linux. Pushed to trunk. Backports needed.

 libstdc++-v3/include/pstl/parallel_backend_tbb.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
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Patch

diff --git a/libstdc++-v3/include/pstl/parallel_backend_tbb.h b/libstdc++-v3/include/pstl/parallel_backend_tbb.h
index bb6fa8f18e83..ff5236f39071 100644
--- a/libstdc++-v3/include/pstl/parallel_backend_tbb.h
+++ b/libstdc++-v3/include/pstl/parallel_backend_tbb.h
@@ -521,7 +521,7 @@  class __root_task
     friend class __func_task<_Func>;
 };
 
-#else  // TBB_INTERFACE_VERSION <= 12000
+#else  // TBB_INTERFACE_VERSION > 12000
 class __task : public tbb::detail::d1::task
 {
   protected:
@@ -656,10 +656,16 @@  class __func_task : public __task
 
         _PSTL_ASSERT(__parent != nullptr);
         _PSTL_ASSERT(__parent->_M_refcount.load(std::memory_order_relaxed) > 0);
-        if (--__parent->_M_refcount == 0)
+
+        auto __refcount = --__parent->_M_refcount;
+
+        // Placing the deallocation after the refcount decrement allows another thread to proceed with tree
+        // folding concurrently with this task cleanup.
+        __alloc.deallocate(this, *__ed);
+
+        if (__refcount == 0)
         {
             _PSTL_ASSERT(__next == nullptr);
-            __alloc.deallocate(this, *__ed);
             return __parent;
         }