gh-145846: Fix memory leak in _lsprof clearEntries() context chain

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)
+
+        p = _lsprof.Profiler()
+        p.enable()
+        for _ in range(100):
+            level1(p)
+        p.disable()
+        p.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 *c = pObj->currentProfilerContext;
+        pObj->currentProfilerContext = c->previous;
+        PyMem_Free(c);
     }
     while (pObj->freelistProfilerContext) {
         ProfilerContext *c = pObj->freelistProfilerContext;