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gh-130030: Fix crash on 32-bit Linux with free threading #130043

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Merged
merged 2 commits into from
Feb 12, 2025
Merged

gh-130030: Fix crash on 32-bit Linux with free threading #130043

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gh-130030: Fix crash on 32-bit Linux with free threading
colesbury Feb 12, 2025
a79d4a6
Switch back to unsigned int
colesbury Feb 12, 2025
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12 changes: 6 additions & 6 deletions Objects/obmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3297,12 +3297,12 @@ static bool _collect_alloc_stats(
static void
py_mimalloc_print_stats(FILE *out)
{
fprintf(out, "Small block threshold = %zd, in %u size classes.\n",
MI_SMALL_OBJ_SIZE_MAX, MI_BIN_HUGE);
fprintf(out, "Medium block threshold = %zd\n",
MI_MEDIUM_OBJ_SIZE_MAX);
fprintf(out, "Large object max size = %zd\n",
MI_LARGE_OBJ_SIZE_MAX);
fprintf(out, "Small block threshold = %zu, in %u size classes.\n",
(size_t)MI_SMALL_OBJ_SIZE_MAX, MI_BIN_HUGE);
fprintf(out, "Medium block threshold = %zu\n",
(size_t)MI_MEDIUM_OBJ_SIZE_MAX);
fprintf(out, "Large object max size = %zu\n",
(size_t)MI_LARGE_OBJ_SIZE_MAX);

mi_heap_t *heap = mi_heap_get_default();
struct _alloc_stats stats;
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14 changes: 7 additions & 7 deletions Python/gc_free_threading.c
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Original file line number Diff line number Diff line change
Expand Up @@ -564,8 +564,8 @@ typedef struct {
} gc_span_stack_t;

typedef struct {
unsigned int in;
unsigned int out;
Py_ssize_t in;
Py_ssize_t out;
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Warnings could also be fixed by changing this line:

Py_ssize_t space = BUFFER_HI - gc_mark_buffer_len(args);

to

unsigned int space = BUFFER_HI - gc_mark_buffer_len(args);

The assert should be changed in that case, since size can't be negative.

assert(space <= gc_mark_buffer_avail(args));
assert(space <= BUFFER_HI);

Performance wise I would doubt that using Py_ssize_t makes any difference. On 32-bit platforms maybe a little since it would use a 64-bit int rather than a 32-bit one?

I would still prefer to use the unsigned integer types since my understanding is that the C standard defines overflow behavior for unsigned integers but not signed ones. The buffer "in" and "out" calculations depend on the overflow behavior.

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That makes sense -- I switched back to unsigned int.

On 32-bit platforms maybe a little since it would use a 64-bit int rather than a 32-bit one?

Py_ssize_t is the same size as size_t, so typically 32-bits on a 32-bit platform.

_PyObjectStack stack;
gc_span_stack_t spans;
PyObject *buffer[BUFFER_SIZE];
Expand All @@ -574,14 +574,14 @@ typedef struct {


// Returns number of entries in buffer
static inline unsigned int
static inline Py_ssize_t
gc_mark_buffer_len(gc_mark_args_t *args)
{
return args->in - args->out;
}

// Returns number of free entry slots in buffer
static inline unsigned int
static inline Py_ssize_t
gc_mark_buffer_avail(gc_mark_args_t *args)
{
return BUFFER_SIZE - gc_mark_buffer_len(args);
Expand Down Expand Up @@ -1074,14 +1074,14 @@ mark_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
return true;
}

_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");

if (gc_is_alive(op) || !gc_is_unreachable(op)) {
// Object was already marked as reachable.
return true;
}

_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");

// GH-129236: If we've seen an active frame without a valid stack pointer,
// then we can't collect objects with deferred references because we may
// have missed some reference to the object on the stack. In that case,
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