bpo-40609: _tracemalloc allocates traces (GH-20064)

Rewrite _tracemalloc to store "trace_t*" rather than directly
"trace_t" in traces hash tables. Traces are now allocated on the heap
memory, outside the hash table.

Add tracemalloc_copy_traces() and tracemalloc_copy_domains() helper
functions.

Remove _Py_hashtable_copy() function since there is no API to copy a
key or a value.

Remove also _Py_hashtable_delete() function which was commented.

Include/internal/pycore_hashtable.h

@@ -45,13 +45,6 @@ typedef struct {
                   sizeof(DATA)); \
     } while (0)
 
-#define _Py_HASHTABLE_ENTRY_WRITE_DATA(TABLE, ENTRY, DATA) \
-    do { \
-        assert(sizeof(DATA) == (TABLE)->data_size); \
-        memcpy((void *)_Py_HASHTABLE_ENTRY_PDATA(ENTRY), \
-                  &(DATA), sizeof(DATA)); \
-    } while (0)
-
 
 /* _Py_hashtable: prototypes */
 
@@ -118,9 +111,6 @@ PyAPI_FUNC(_Py_hashtable_t *) _Py_hashtable_new_full(
 
 PyAPI_FUNC(void) _Py_hashtable_destroy(_Py_hashtable_t *ht);
 
-/* Return a copy of the hash table */
-PyAPI_FUNC(_Py_hashtable_t *) _Py_hashtable_copy(_Py_hashtable_t *src);
-
 PyAPI_FUNC(void) _Py_hashtable_clear(_Py_hashtable_t *ht);
 
 typedef int (*_Py_hashtable_foreach_func) (_Py_hashtable_t *ht,

Modules/_tracemalloc.c

@@ -122,7 +122,7 @@ static traceback_t *tracemalloc_traceback = NULL;
    Protected by the GIL */
 static _Py_hashtable_t *tracemalloc_tracebacks = NULL;
 
-/* pointer (void*) => trace (trace_t).
+/* pointer (void*) => trace (trace_t*).
    Protected by TABLES_LOCK(). */
 static _Py_hashtable_t *tracemalloc_traces = NULL;
 
@@ -467,13 +467,23 @@ traceback_new(void)
 }
 
 
+static void
+tracemalloc_destroy_trace_cb(_Py_hashtable_t *traces,
+                             _Py_hashtable_entry_t *entry)
+{
+    trace_t *trace;
+    _Py_HASHTABLE_ENTRY_READ_DATA(traces, entry, trace);
+    raw_free(trace);
+}
+
+
 static _Py_hashtable_t*
 tracemalloc_create_traces_table(void)
 {
-    return hashtable_new(sizeof(trace_t),
+    return hashtable_new(sizeof(trace_t*),
                          _Py_hashtable_hash_ptr,
                          _Py_hashtable_compare_direct,
-                         NULL);
+                         tracemalloc_destroy_trace_cb);
 }
 
 
@@ -528,12 +538,13 @@ tracemalloc_remove_trace(unsigned int domain, uintptr_t ptr)
         return;
     }
 
-    trace_t trace;
+    trace_t *trace;
     if (!_Py_HASHTABLE_POP(traces, TO_PTR(ptr), trace)) {
         return;
     }
-    assert(tracemalloc_traced_memory >= trace.size);
+    assert(tracemalloc_traced_memory >= trace->size);
-    tracemalloc_traced_memory -= trace.size;
+    tracemalloc_traced_memory -= trace->size;
+    raw_free(trace);
 }
 
 #define REMOVE_TRACE(ptr) \
@@ -565,23 +576,27 @@ tracemalloc_add_trace(unsigned int domain, uintptr_t ptr,
     }
 
     _Py_hashtable_entry_t* entry = _Py_HASHTABLE_GET_ENTRY(traces, ptr);
-    trace_t trace;
     if (entry != NULL) {
         /* the memory block is already tracked */
+        trace_t *trace;
         _Py_HASHTABLE_ENTRY_READ_DATA(traces, entry, trace);
-        assert(tracemalloc_traced_memory >= trace.size);
+        assert(tracemalloc_traced_memory >= trace->size);
-        tracemalloc_traced_memory -= trace.size;
+        tracemalloc_traced_memory -= trace->size;
 
-        trace.size = size;
+        trace->size = size;
-        trace.traceback = traceback;
+        trace->traceback = traceback;
-        _Py_HASHTABLE_ENTRY_WRITE_DATA(traces, entry, trace);
     }
     else {
-        trace.size = size;
+        trace_t *trace = raw_malloc(sizeof(trace_t));
-        trace.traceback = traceback;
+        if (trace == NULL) {
+            return -1;
+        }
+        trace->size = size;
+        trace->traceback = traceback;
 
         int res = _Py_HASHTABLE_SET(traces, TO_PTR(ptr), trace);
         if (res != 0) {
+            raw_free(trace);
             return res;
         }
     }
@@ -1225,19 +1240,62 @@ typedef struct {
     unsigned int domain;
 } get_traces_t;
 
+
 static int
-tracemalloc_get_traces_copy_domain(_Py_hashtable_t *domains,
+tracemalloc_copy_trace(_Py_hashtable_t *traces,
                        _Py_hashtable_entry_t *entry,
-                                   void *user_data)
+                       void *traces2_raw)
 {
-    get_traces_t *get_traces = user_data;
+    _Py_hashtable_t *traces2 = (_Py_hashtable_t *)traces2_raw;
+
+    trace_t *trace;
+    _Py_HASHTABLE_ENTRY_READ_DATA(traces, entry, trace);
+
+    trace_t *trace2 = raw_malloc(sizeof(trace_t));
+    if (traces2 == NULL) {
+        return -1;
+    }
+    *trace2 = *trace;
+    if (_Py_HASHTABLE_SET(traces2, entry->key, trace2) < 0) {
+        raw_free(trace2);
+        return -1;
+    }
+    return 0;
+}
+
+
+static _Py_hashtable_t*
+tracemalloc_copy_traces(_Py_hashtable_t *traces)
+{
+    _Py_hashtable_t *traces2 = tracemalloc_create_traces_table();
+    if (traces2 == NULL) {
+        return NULL;
+    }
+
+    int err = _Py_hashtable_foreach(traces,
+                                    tracemalloc_copy_trace,
+                                    traces2);
+    if (err) {
+        _Py_hashtable_destroy(traces2);
+        return NULL;
+    }
+    return traces2;
+}
+
+
+static int
+tracemalloc_copy_domain(_Py_hashtable_t *domains,
+                        _Py_hashtable_entry_t *entry,
+                        void *domains2_raw)
+{
+    _Py_hashtable_t *domains2 = (_Py_hashtable_t *)domains2_raw;
 
     unsigned int domain = (unsigned int)FROM_PTR(entry->key);
     _Py_hashtable_t *traces;
     _Py_HASHTABLE_ENTRY_READ_DATA(domains, entry, traces);
 
-    _Py_hashtable_t *traces2 = _Py_hashtable_copy(traces);
+    _Py_hashtable_t *traces2 = tracemalloc_copy_traces(traces);
-    if (_Py_HASHTABLE_SET(get_traces->domains, TO_PTR(domain), traces2) < 0) {
+    if (_Py_HASHTABLE_SET(domains2, TO_PTR(domain), traces2) < 0) {
         _Py_hashtable_destroy(traces2);
         return -1;
     }
@@ -1245,18 +1303,37 @@ tracemalloc_get_traces_copy_domain(_Py_hashtable_t *domains,
 }
 
 
+static _Py_hashtable_t*
+tracemalloc_copy_domains(_Py_hashtable_t *domains)
+{
+    _Py_hashtable_t *domains2 = tracemalloc_create_domains_table();
+    if (domains2 == NULL) {
+        return NULL;
+    }
+
+    int err = _Py_hashtable_foreach(domains,
+                                    tracemalloc_copy_domain,
+                                    domains2);
+    if (err) {
+        _Py_hashtable_destroy(domains2);
+        return NULL;
+    }
+    return domains2;
+}
+
+
 static int
 tracemalloc_get_traces_fill(_Py_hashtable_t *traces, _Py_hashtable_entry_t *entry,
                             void *user_data)
 {
     get_traces_t *get_traces = user_data;
-    trace_t trace;
+    trace_t *trace;
     PyObject *tracemalloc_obj;
     int res;
 
     _Py_HASHTABLE_ENTRY_READ_DATA(traces, entry, trace);
 
-    tracemalloc_obj = trace_to_pyobject(get_traces->domain, &trace, get_traces->tracebacks);
+    tracemalloc_obj = trace_to_pyobject(get_traces->domain, trace, get_traces->tracebacks);
     if (tracemalloc_obj == NULL)
         return 1;
 
@@ -1335,37 +1412,34 @@ _tracemalloc__get_traces_impl(PyObject *module)
         goto no_memory;
     }
 
-    get_traces.domains = tracemalloc_create_domains_table();
-    if (get_traces.domains == NULL) {
-        goto no_memory;
-    }
-
-    int err;
-
     // Copy all traces so tracemalloc_get_traces_fill() doesn't have to disable
     // temporarily tracemalloc which would impact other threads and so would
     // miss allocations while get_traces() is called.
     TABLES_LOCK();
-    get_traces.traces = _Py_hashtable_copy(tracemalloc_traces);
+    get_traces.traces = tracemalloc_copy_traces(tracemalloc_traces);
-    err = _Py_hashtable_foreach(tracemalloc_domains,
-                                tracemalloc_get_traces_copy_domain,
-                                &get_traces);
     TABLES_UNLOCK();
 
     if (get_traces.traces == NULL) {
         goto no_memory;
     }
-    if (err) {
+
+    TABLES_LOCK();
+    get_traces.domains = tracemalloc_copy_domains(tracemalloc_domains);
+    TABLES_UNLOCK();
+
+    if (get_traces.domains == NULL) {
         goto no_memory;
     }
 
     // Convert traces to a list of tuples
     set_reentrant(1);
-    err = _Py_hashtable_foreach(get_traces.traces,
+    int err = _Py_hashtable_foreach(get_traces.traces,
-                                tracemalloc_get_traces_fill, &get_traces);
+                                    tracemalloc_get_traces_fill,
+                                    &get_traces);
     if (!err) {
         err = _Py_hashtable_foreach(get_traces.domains,
-                                    tracemalloc_get_traces_domain, &get_traces);
+                                    tracemalloc_get_traces_domain,
+                                    &get_traces);
     }
     set_reentrant(0);
     if (err) {
@@ -1398,7 +1472,7 @@ finally:
 static traceback_t*
 tracemalloc_get_traceback(unsigned int domain, uintptr_t ptr)
 {
-    trace_t trace;
+    trace_t *trace;
     int found;
 
     if (!_Py_tracemalloc_config.tracing)
@@ -1414,10 +1488,11 @@ tracemalloc_get_traceback(unsigned int domain, uintptr_t ptr)
     }
     TABLES_UNLOCK();
 
-    if (!found)
+    if (!found) {
         return NULL;
+    }
 
-    return trace.traceback;
+    return trace->traceback;
 }
 
 
@@ -1758,10 +1833,9 @@ _PyTraceMalloc_NewReference(PyObject *op)
         /* update the traceback of the memory block */
         traceback_t *traceback = traceback_new();
         if (traceback != NULL) {
-            trace_t trace;
+            trace_t *trace;
             _Py_HASHTABLE_ENTRY_READ_DATA(tracemalloc_traces, entry, trace);
-            trace.traceback = traceback;
+            trace->traceback = traceback;
-            _Py_HASHTABLE_ENTRY_WRITE_DATA(tracemalloc_traces, entry, trace);
             res = 0;
         }
     }

Python/hashtable.c

@@ -350,21 +350,6 @@ _Py_hashtable_pop(_Py_hashtable_t *ht, const void *key,
 }
 
 
-/* Code commented since the function is not needed in Python */
-#if 0
-void
-_Py_hashtable_delete(_Py_hashtable_t *ht, size_t const void *key)
-{
-#ifndef NDEBUG
-    int found = _Py_hashtable_pop_entry(ht, key, NULL, 0);
-    assert(found);
-#else
-    (void)_Py_hashtable_pop_entry(ht, key, NULL, 0);
-#endif
-}
-#endif
-
-
 int
 _Py_hashtable_foreach(_Py_hashtable_t *ht,
                       _Py_hashtable_foreach_func func,
@@ -538,37 +523,3 @@ _Py_hashtable_destroy(_Py_hashtable_t *ht)
     ht->alloc.free(ht->buckets);
     ht->alloc.free(ht);
 }
-
-
-_Py_hashtable_t *
-_Py_hashtable_copy(_Py_hashtable_t *src)
-{
-    const size_t data_size = src->data_size;
-    _Py_hashtable_t *dst;
-    _Py_hashtable_entry_t *entry;
-    size_t bucket;
-    int err;
-
-    dst = _Py_hashtable_new_full(data_size, src->num_buckets,
-                                 src->hash_func,
-                                 src->compare_func,
-                                 src->key_destroy_func,
-                                 src->value_destroy_func,
-                                 &src->alloc);
-    if (dst == NULL)
-        return NULL;
-
-    for (bucket=0; bucket < src->num_buckets; bucket++) {
-        entry = TABLE_HEAD(src, bucket);
-        for (; entry; entry = ENTRY_NEXT(entry)) {
-            const void *key = entry->key;
-            const void *pdata = _Py_HASHTABLE_ENTRY_PDATA(entry);
-            err = _Py_hashtable_set(dst, key, data_size, pdata);
-            if (err) {
-                _Py_hashtable_destroy(dst);
-                return NULL;
-            }
-        }
-    }
-    return dst;
-}