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gh-115491: Keep some fields valid across allocations in obmalloc (free-threading) by colesbury · Pull Request #115745 · python/cpython · GitHub

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gh-115491: Keep some fields valid across allocations in obmalloc (free-threading) #115745

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Merged
DinoV merged 1 commit into from
Feb 21, 2024
Conversation 1 Commits 1 Checks 0 Files changed
Merged

gh-115491: Keep some fields valid across allocations in obmalloc (free-threading) #115745

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12 changes: 6 additions & 6 deletions Objects/object.c
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This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
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Original file line number Diff line number Diff line change
Expand Up @@ -299,13 +299,13 @@ _Py_DecRef(PyObject *o)

#ifdef Py_GIL_DISABLED
# ifdef Py_REF_DEBUG
static inline int
is_shared_refcnt_dead(Py_ssize_t shared)
static int
is_dead(PyObject *o)
{
# if SIZEOF_SIZE_T == 8
return shared == (Py_ssize_t)0xDDDDDDDDDDDDDDDD;
return (uintptr_t)o->ob_type == 0xDDDDDDDDDDDDDDDD;
# else
return shared == (Py_ssize_t)0xDDDDDDDD;
return (uintptr_t)o->ob_type == 0xDDDDDDDD;
# endif
}
# endif
Expand Down Expand Up @@ -335,8 +335,8 @@ _Py_DecRefSharedDebug(PyObject *o, const char *filename, int lineno)
}

#ifdef Py_REF_DEBUG
if ((_Py_REF_IS_MERGED(new_shared) && new_shared < 0) ||
is_shared_refcnt_dead(shared))
if ((new_shared < 0 && _Py_REF_IS_MERGED(new_shared)) ||
(should_queue && is_dead(o)))
{
_Py_NegativeRefcount(filename, lineno, o);
}
Expand Down
31 changes: 27 additions & 4 deletions Objects/obmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2459,6 +2459,24 @@ write_size_t(void *p, size_t n)
}
}

static void
fill_mem_debug(debug_alloc_api_t *api, void *data, int c, size_t nbytes)
{
#ifdef Py_GIL_DISABLED
if (api->api_id == 'o') {
// Don't overwrite the first few bytes of a PyObject allocation in the
// free-threaded build
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
size_t debug_offset = tstate->mimalloc.current_object_heap->debug_offset;
if (debug_offset < nbytes) {
memset((char *)data + debug_offset, c, nbytes - debug_offset);
}
return;
}
#endif
memset(data, c, nbytes);
}

/* Let S = sizeof(size_t). The debug malloc asks for 4 * S extra bytes and
fills them with useful stuff, here calling the underlying malloc's result p:

Expand Down Expand Up @@ -2535,7 +2553,7 @@ _PyMem_DebugRawAlloc(int use_calloc, void *ctx, size_t nbytes)
memset(p + SST + 1, PYMEM_FORBIDDENBYTE, SST-1);

if (nbytes > 0 && !use_calloc) {
memset(data, PYMEM_CLEANBYTE, nbytes);
fill_mem_debug(api, data, PYMEM_CLEANBYTE, nbytes);
}

/* at tail, write pad (SST bytes) and serialno (SST bytes) */
Expand Down Expand Up @@ -2583,8 +2601,9 @@ _PyMem_DebugRawFree(void *ctx, void *p)

_PyMem_DebugCheckAddress(__func__, api->api_id, p);
nbytes = read_size_t(q);
nbytes += PYMEM_DEBUG_EXTRA_BYTES;
memset(q, PYMEM_DEADBYTE, nbytes);
nbytes += PYMEM_DEBUG_EXTRA_BYTES - 2*SST;
memset(q, PYMEM_DEADBYTE, 2*SST);
fill_mem_debug(api, p, PYMEM_DEADBYTE, nbytes);
api->alloc.free(api->alloc.ctx, q);
}

Expand All @@ -2604,7 +2623,6 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
size_t total; /* 2 * SST + nbytes + 2 * SST */
size_t original_nbytes;
#define ERASED_SIZE 64
uint8_t save[2*ERASED_SIZE]; /* A copy of erased bytes. */

_PyMem_DebugCheckAddress(__func__, api->api_id, p);

Expand All @@ -2621,9 +2639,11 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
#ifdef PYMEM_DEBUG_SERIALNO
size_t block_serialno = read_size_t(tail + SST);
#endif
#ifndef Py_GIL_DISABLED
/* Mark the header, the trailer, ERASED_SIZE bytes at the begin and
ERASED_SIZE bytes at the end as dead and save the copy of erased bytes.
*/
uint8_t save[2*ERASED_SIZE]; /* A copy of erased bytes. */
if (original_nbytes <= sizeof(save)) {
memcpy(save, data, original_nbytes);
memset(data - 2 * SST, PYMEM_DEADBYTE,
Expand All @@ -2636,6 +2656,7 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
memset(tail - ERASED_SIZE, PYMEM_DEADBYTE,
ERASED_SIZE + PYMEM_DEBUG_EXTRA_BYTES - 2 * SST);
}
#endif

/* Resize and add decorations. */
r = (uint8_t *)api->alloc.realloc(api->alloc.ctx, head, total);
Expand Down Expand Up @@ -2663,6 +2684,7 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
write_size_t(tail + SST, block_serialno);
#endif

#ifndef Py_GIL_DISABLED
/* Restore saved bytes. */
if (original_nbytes <= sizeof(save)) {
memcpy(data, save, Py_MIN(nbytes, original_nbytes));
Expand All @@ -2675,6 +2697,7 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
Py_MIN(nbytes - i, ERASED_SIZE));
}
}
#endif

if (r == NULL) {
return NULL;
Expand Down
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