pythongh-145846: Fix memory leak in _lsprof clearEntries() context chain (python#145847)

clearEntries() only freed the top currentProfilerContext but did not
walk the previous linked list. When clear() is called during active
profiling with nested calls, all contexts except the top one were
leaked. Fix by iterating the entire linked list, matching the existing
freelistProfilerContext cleanup pattern.

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: 2 people

Lib/test/test_profiling/test_tracing_profiler.py

@@ -142,6 +142,28 @@ def gen():
 
         self.assertTrue(any("throw" in func[2] for func in pr.stats.keys())),
 
+    def test_clear_with_nested_calls(self):
+        # Calling clear() during nested profiled calls should not leak
+        # ProfilerContexts. clearEntries() must walk the entire linked list,
+        # not just free the top context.
+        import _lsprof
+
+        def level3(profiler):
+            profiler.clear()
+
+        def level2(profiler):
+            level3(profiler)
+
+        def level1(profiler):
+            level2(profiler)
+
+        profiler = _lsprof.Profiler()
+        profiler.enable()
+        for _ in range(100):
+            level1(profiler)
+        profiler.disable()
+        profiler.clear()
+
     def test_bad_descriptor(self):
         # gh-132250
         # cProfile should not crash when the profiler callback fails to locate

Misc/NEWS.d/next/Library/2026-03-12-00-00-00.gh-issue-145846.UbHxjv.rst

@@ -0,0 +1,3 @@
+Fix memory leak in ``_lsprof`` when ``clear()`` is called during active
+profiling with nested calls. ``clearEntries()`` now walks the entire
+``currentProfilerContext`` linked list instead of only freeing the top context.

Modules/_lsprof.c

@@ -292,9 +292,10 @@ static void clearEntries(ProfilerObject *pObj)
     RotatingTree_Enum(pObj->profilerEntries, freeEntry, NULL);
     pObj->profilerEntries = EMPTY_ROTATING_TREE;
     /* release the memory hold by the ProfilerContexts */
-    if (pObj->currentProfilerContext) {
-        PyMem_Free(pObj->currentProfilerContext);
-        pObj->currentProfilerContext = NULL;
+    while (pObj->currentProfilerContext) {
+        ProfilerContext *pContext = pObj->currentProfilerContext;
+        pObj->currentProfilerContext = pContext->previous;
+        PyMem_Free(pContext);
     }
     while (pObj->freelistProfilerContext) {
         ProfilerContext *c = pObj->freelistProfilerContext;