1/* Malloc implementation for multiple threads without lock contention.
2 Copyright (C) 2001-2016 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If
18 not, see <http://www.gnu.org/licenses/>. */
19
20#include <stdbool.h>
21
22/* Compile-time constants. */
23
24#define HEAP_MIN_SIZE (32 * 1024)
25#ifndef HEAP_MAX_SIZE
26# ifdef DEFAULT_MMAP_THRESHOLD_MAX
27# define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX)
28# else
29# define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */
30# endif
31#endif
32
33/* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps
34 that are dynamically created for multi-threaded programs. The
35 maximum size must be a power of two, for fast determination of
36 which heap belongs to a chunk. It should be much larger than the
37 mmap threshold, so that requests with a size just below that
38 threshold can be fulfilled without creating too many heaps. */
39
40/***************************************************************************/
41
42#define top(ar_ptr) ((ar_ptr)->top)
43
44/* A heap is a single contiguous memory region holding (coalesceable)
45 malloc_chunks. It is allocated with mmap() and always starts at an
46 address aligned to HEAP_MAX_SIZE. */
47
48typedef struct _heap_info
49{
50 mstate ar_ptr; /* Arena for this heap. */
51 struct _heap_info *prev; /* Previous heap. */
52 size_t size; /* Current size in bytes. */
53 size_t mprotect_size; /* Size in bytes that has been mprotected
54 PROT_READ|PROT_WRITE. */
55 /* Make sure the following data is properly aligned, particularly
56 that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of
57 MALLOC_ALIGNMENT. */
58 char pad[-6 * SIZE_SZ & MALLOC_ALIGN_MASK];
59} heap_info;
60
61/* Get a compile-time error if the heap_info padding is not correct
62 to make alignment work as expected in sYSMALLOc. */
63extern int sanity_check_heap_info_alignment[(sizeof (heap_info)
64 + 2 * SIZE_SZ) % MALLOC_ALIGNMENT
65 ? -1 : 1];
66
67/* Thread specific data. */
68
69static __thread mstate thread_arena attribute_tls_model_ie;
70
71/* Arena free list. free_list_lock synchronizes access to the
72 free_list variable below, and the next_free and attached_threads
73 members of struct malloc_state objects. No other locks must be
74 acquired after free_list_lock has been acquired. */
75
76static mutex_t free_list_lock = _LIBC_LOCK_INITIALIZER;
77static size_t narenas = 1;
78static mstate free_list;
79
80/* list_lock prevents concurrent writes to the next member of struct
81 malloc_state objects.
82
83 Read access to the next member is supposed to synchronize with the
84 atomic_write_barrier and the write to the next member in
85 _int_new_arena. This suffers from data races; see the FIXME
86 comments in _int_new_arena and reused_arena.
87
88 list_lock also prevents concurrent forks. At the time list_lock is
89 acquired, no arena lock must have been acquired, but it is
90 permitted to acquire arena locks subsequently, while list_lock is
91 acquired. */
92static mutex_t list_lock = _LIBC_LOCK_INITIALIZER;
93
94/* Mapped memory in non-main arenas (reliable only for NO_THREADS). */
95static unsigned long arena_mem;
96
97/* Already initialized? */
98int __malloc_initialized = -1;
99
100/**************************************************************************/
101
102
103/* arena_get() acquires an arena and locks the corresponding mutex.
104 First, try the one last locked successfully by this thread. (This
105 is the common case and handled with a macro for speed.) Then, loop
106 once over the circularly linked list of arenas. If no arena is
107 readily available, create a new one. In this latter case, `size'
108 is just a hint as to how much memory will be required immediately
109 in the new arena. */
110
111#define arena_get(ptr, size) do { \
112 ptr = thread_arena; \
113 arena_lock (ptr, size); \
114 } while (0)
115
116#define arena_lock(ptr, size) do { \
117 if (ptr && !arena_is_corrupt (ptr)) \
118 (void) mutex_lock (&ptr->mutex); \
119 else \
120 ptr = arena_get2 ((size), NULL); \
121 } while (0)
122
123/* find the heap and corresponding arena for a given ptr */
124
125#define heap_for_ptr(ptr) \
126 ((heap_info *) ((unsigned long) (ptr) & ~(HEAP_MAX_SIZE - 1)))
127#define arena_for_chunk(ptr) \
128 (chunk_non_main_arena (ptr) ? heap_for_ptr (ptr)->ar_ptr : &main_arena)
129
130
131/**************************************************************************/
132
133/* atfork support. */
134
135/* The following three functions are called around fork from a
136 multi-threaded process. We do not use the general fork handler
137 mechanism to make sure that our handlers are the last ones being
138 called, so that other fork handlers can use the malloc
139 subsystem. */
140
141void
142internal_function
143__malloc_fork_lock_parent (void)
144{
145 if (__malloc_initialized < 1)
146 return;
147
148 /* We do not acquire free_list_lock here because we completely
149 reconstruct free_list in __malloc_fork_unlock_child. */
150
151 (void) mutex_lock (&list_lock);
152
153 for (mstate ar_ptr = &main_arena;; )
154 {
155 (void) mutex_lock (&ar_ptr->mutex);
156 ar_ptr = ar_ptr->next;
157 if (ar_ptr == &main_arena)
158 break;
159 }
160}
161
162void
163internal_function
164__malloc_fork_unlock_parent (void)
165{
166 if (__malloc_initialized < 1)
167 return;
168
169 for (mstate ar_ptr = &main_arena;; )
170 {
171 (void) mutex_unlock (&ar_ptr->mutex);
172 ar_ptr = ar_ptr->next;
173 if (ar_ptr == &main_arena)
174 break;
175 }
176 (void) mutex_unlock (&list_lock);
177}
178
179void
180internal_function
181__malloc_fork_unlock_child (void)
182{
183 if (__malloc_initialized < 1)
184 return;
185
186 /* Push all arenas to the free list, except thread_arena, which is
187 attached to the current thread. */
188 mutex_init (&free_list_lock);
189 if (thread_arena != NULL)
190 thread_arena->attached_threads = 1;
191 free_list = NULL;
192 for (mstate ar_ptr = &main_arena;; )
193 {
194 mutex_init (&ar_ptr->mutex);
195 if (ar_ptr != thread_arena)
196 {
197 /* This arena is no longer attached to any thread. */
198 ar_ptr->attached_threads = 0;
199 ar_ptr->next_free = free_list;
200 free_list = ar_ptr;
201 }
202 ar_ptr = ar_ptr->next;
203 if (ar_ptr == &main_arena)
204 break;
205 }
206
207 mutex_init (&list_lock);
208}
209
210/* Initialization routine. */
211#include <string.h>
212extern char **_environ;
213
214static char *
215internal_function
216next_env_entry (char ***position)
217{
218 char **current = *position;
219 char *result = NULL;
220
221 while (*current != NULL)
222 {
223 if (__builtin_expect ((*current)[0] == 'M', 0)
224 && (*current)[1] == 'A'
225 && (*current)[2] == 'L'
226 && (*current)[3] == 'L'
227 && (*current)[4] == 'O'
228 && (*current)[5] == 'C'
229 && (*current)[6] == '_')
230 {
231 result = &(*current)[7];
232
233 /* Save current position for next visit. */
234 *position = ++current;
235
236 break;
237 }
238
239 ++current;
240 }
241
242 return result;
243}
244
245
246#ifdef SHARED
247static void *
248__failing_morecore (ptrdiff_t d)
249{
250 return (void *) MORECORE_FAILURE;
251}
252
253extern struct dl_open_hook *_dl_open_hook;
254libc_hidden_proto (_dl_open_hook);
255#endif
256
257static void
258ptmalloc_init (void)
259{
260 if (__malloc_initialized >= 0)
261 return;
262
263 __malloc_initialized = 0;
264
265#ifdef SHARED
266 /* In case this libc copy is in a non-default namespace, never use brk.
267 Likewise if dlopened from statically linked program. */
268 Dl_info di;
269 struct link_map *l;
270
271 if (_dl_open_hook != NULL
272 || (_dl_addr (ptmalloc_init, &di, &l, NULL) != 0
273 && l->l_ns != LM_ID_BASE))
274 __morecore = __failing_morecore;
275#endif
276
277 thread_arena = &main_arena;
278 const char *s = NULL;
279 if (__glibc_likely (_environ != NULL))
280 {
281 char **runp = _environ;
282 char *envline;
283
284 while (__builtin_expect ((envline = next_env_entry (&runp)) != NULL,
285 0))
286 {
287 size_t len = strcspn (envline, "=");
288
289 if (envline[len] != '=')
290 /* This is a "MALLOC_" variable at the end of the string
291 without a '=' character. Ignore it since otherwise we
292 will access invalid memory below. */
293 continue;
294
295 switch (len)
296 {
297 case 6:
298 if (memcmp (envline, "CHECK_", 6) == 0)
299 s = &envline[7];
300 break;
301 case 8:
302 if (!__builtin_expect (__libc_enable_secure, 0))
303 {
304 if (memcmp (envline, "TOP_PAD_", 8) == 0)
305 __libc_mallopt (M_TOP_PAD, atoi (&envline[9]));
306 else if (memcmp (envline, "PERTURB_", 8) == 0)
307 __libc_mallopt (M_PERTURB, atoi (&envline[9]));
308 }
309 break;
310 case 9:
311 if (!__builtin_expect (__libc_enable_secure, 0))
312 {
313 if (memcmp (envline, "MMAP_MAX_", 9) == 0)
314 __libc_mallopt (M_MMAP_MAX, atoi (&envline[10]));
315 else if (memcmp (envline, "ARENA_MAX", 9) == 0)
316 __libc_mallopt (M_ARENA_MAX, atoi (&envline[10]));
317 }
318 break;
319 case 10:
320 if (!__builtin_expect (__libc_enable_secure, 0))
321 {
322 if (memcmp (envline, "ARENA_TEST", 10) == 0)
323 __libc_mallopt (M_ARENA_TEST, atoi (&envline[11]));
324 }
325 break;
326 case 15:
327 if (!__builtin_expect (__libc_enable_secure, 0))
328 {
329 if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0)
330 __libc_mallopt (M_TRIM_THRESHOLD, atoi (&envline[16]));
331 else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0)
332 __libc_mallopt (M_MMAP_THRESHOLD, atoi (&envline[16]));
333 }
334 break;
335 default:
336 break;
337 }
338 }
339 }
340 if (s && s[0])
341 {
342 __libc_mallopt (M_CHECK_ACTION, (int) (s[0] - '0'));
343 if (check_action != 0)
344 __malloc_check_init ();
345 }
346 void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook);
347 if (hook != NULL)
348 (*hook)();
349 __malloc_initialized = 1;
350}
351
352/* Managing heaps and arenas (for concurrent threads) */
353
354#if MALLOC_DEBUG > 1
355
356/* Print the complete contents of a single heap to stderr. */
357
358static void
359dump_heap (heap_info *heap)
360{
361 char *ptr;
362 mchunkptr p;
363
364 fprintf (stderr, "Heap %p, size %10lx:\n", heap, (long) heap->size);
365 ptr = (heap->ar_ptr != (mstate) (heap + 1)) ?
366 (char *) (heap + 1) : (char *) (heap + 1) + sizeof (struct malloc_state);
367 p = (mchunkptr) (((unsigned long) ptr + MALLOC_ALIGN_MASK) &
368 ~MALLOC_ALIGN_MASK);
369 for (;; )
370 {
371 fprintf (stderr, "chunk %p size %10lx", p, (long) p->size);
372 if (p == top (heap->ar_ptr))
373 {
374 fprintf (stderr, " (top)\n");
375 break;
376 }
377 else if (p->size == (0 | PREV_INUSE))
378 {
379 fprintf (stderr, " (fence)\n");
380 break;
381 }
382 fprintf (stderr, "\n");
383 p = next_chunk (p);
384 }
385}
386#endif /* MALLOC_DEBUG > 1 */
387
388/* If consecutive mmap (0, HEAP_MAX_SIZE << 1, ...) calls return decreasing
389 addresses as opposed to increasing, new_heap would badly fragment the
390 address space. In that case remember the second HEAP_MAX_SIZE part
391 aligned to HEAP_MAX_SIZE from last mmap (0, HEAP_MAX_SIZE << 1, ...)
392 call (if it is already aligned) and try to reuse it next time. We need
393 no locking for it, as kernel ensures the atomicity for us - worst case
394 we'll call mmap (addr, HEAP_MAX_SIZE, ...) for some value of addr in
395 multiple threads, but only one will succeed. */
396static char *aligned_heap_area;
397
398/* Create a new heap. size is automatically rounded up to a multiple
399 of the page size. */
400
401static heap_info *
402internal_function
403new_heap (size_t size, size_t top_pad)
404{
405 size_t pagesize = GLRO (dl_pagesize);
406 char *p1, *p2;
407 unsigned long ul;
408 heap_info *h;
409
410 if (size + top_pad < HEAP_MIN_SIZE)
411 size = HEAP_MIN_SIZE;
412 else if (size + top_pad <= HEAP_MAX_SIZE)
413 size += top_pad;
414 else if (size > HEAP_MAX_SIZE)
415 return 0;
416 else
417 size = HEAP_MAX_SIZE;
418 size = ALIGN_UP (size, pagesize);
419
420 /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed.
421 No swap space needs to be reserved for the following large
422 mapping (on Linux, this is the case for all non-writable mappings
423 anyway). */
424 p2 = MAP_FAILED;
425 if (aligned_heap_area)
426 {
427 p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE,
428 MAP_NORESERVE);
429 aligned_heap_area = NULL;
430 if (p2 != MAP_FAILED && ((unsigned long) p2 & (HEAP_MAX_SIZE - 1)))
431 {
432 __munmap (p2, HEAP_MAX_SIZE);
433 p2 = MAP_FAILED;
434 }
435 }
436 if (p2 == MAP_FAILED)
437 {
438 p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, MAP_NORESERVE);
439 if (p1 != MAP_FAILED)
440 {
441 p2 = (char *) (((unsigned long) p1 + (HEAP_MAX_SIZE - 1))
442 & ~(HEAP_MAX_SIZE - 1));
443 ul = p2 - p1;
444 if (ul)
445 __munmap (p1, ul);
446 else
447 aligned_heap_area = p2 + HEAP_MAX_SIZE;
448 __munmap (p2 + HEAP_MAX_SIZE, HEAP_MAX_SIZE - ul);
449 }
450 else
451 {
452 /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
453 is already aligned. */
454 p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, MAP_NORESERVE);
455 if (p2 == MAP_FAILED)
456 return 0;
457
458 if ((unsigned long) p2 & (HEAP_MAX_SIZE - 1))
459 {
460 __munmap (p2, HEAP_MAX_SIZE);
461 return 0;
462 }
463 }
464 }
465 if (__mprotect (p2, size, PROT_READ | PROT_WRITE) != 0)
466 {
467 __munmap (p2, HEAP_MAX_SIZE);
468 return 0;
469 }
470 h = (heap_info *) p2;
471 h->size = size;
472 h->mprotect_size = size;
473 LIBC_PROBE (memory_heap_new, 2, h, h->size);
474 return h;
475}
476
477/* Grow a heap. size is automatically rounded up to a
478 multiple of the page size. */
479
480static int
481grow_heap (heap_info *h, long diff)
482{
483 size_t pagesize = GLRO (dl_pagesize);
484 long new_size;
485
486 diff = ALIGN_UP (diff, pagesize);
487 new_size = (long) h->size + diff;
488 if ((unsigned long) new_size > (unsigned long) HEAP_MAX_SIZE)
489 return -1;
490
491 if ((unsigned long) new_size > h->mprotect_size)
492 {
493 if (__mprotect ((char *) h + h->mprotect_size,
494 (unsigned long) new_size - h->mprotect_size,
495 PROT_READ | PROT_WRITE) != 0)
496 return -2;
497
498 h->mprotect_size = new_size;
499 }
500
501 h->size = new_size;
502 LIBC_PROBE (memory_heap_more, 2, h, h->size);
503 return 0;
504}
505
506/* Shrink a heap. */
507
508static int
509shrink_heap (heap_info *h, long diff)
510{
511 long new_size;
512
513 new_size = (long) h->size - diff;
514 if (new_size < (long) sizeof (*h))
515 return -1;
516
517 /* Try to re-map the extra heap space freshly to save memory, and make it
518 inaccessible. See malloc-sysdep.h to know when this is true. */
519 if (__glibc_unlikely (check_may_shrink_heap ()))
520 {
521 if ((char *) MMAP ((char *) h + new_size, diff, PROT_NONE,
522 MAP_FIXED) == (char *) MAP_FAILED)
523 return -2;
524
525 h->mprotect_size = new_size;
526 }
527 else
528 __madvise ((char *) h + new_size, diff, MADV_DONTNEED);
529 /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
530
531 h->size = new_size;
532 LIBC_PROBE (memory_heap_less, 2, h, h->size);
533 return 0;
534}
535
536/* Delete a heap. */
537
538#define delete_heap(heap) \
539 do { \
540 if ((char *) (heap) + HEAP_MAX_SIZE == aligned_heap_area) \
541 aligned_heap_area = NULL; \
542 __munmap ((char *) (heap), HEAP_MAX_SIZE); \
543 } while (0)
544
545static int
546internal_function
547heap_trim (heap_info *heap, size_t pad)
548{
549 mstate ar_ptr = heap->ar_ptr;
550 unsigned long pagesz = GLRO (dl_pagesize);
551 mchunkptr top_chunk = top (ar_ptr), p, bck, fwd;
552 heap_info *prev_heap;
553 long new_size, top_size, top_area, extra, prev_size, misalign;
554
555 /* Can this heap go away completely? */
556 while (top_chunk == chunk_at_offset (heap, sizeof (*heap)))
557 {
558 prev_heap = heap->prev;
559 prev_size = prev_heap->size - (MINSIZE - 2 * SIZE_SZ);
560 p = chunk_at_offset (prev_heap, prev_size);
561 /* fencepost must be properly aligned. */
562 misalign = ((long) p) & MALLOC_ALIGN_MASK;
563 p = chunk_at_offset (prev_heap, prev_size - misalign);
564 assert (p->size == (0 | PREV_INUSE)); /* must be fencepost */
565 p = prev_chunk (p);
566 new_size = chunksize (p) + (MINSIZE - 2 * SIZE_SZ) + misalign;
567 assert (new_size > 0 && new_size < (long) (2 * MINSIZE));
568 if (!prev_inuse (p))
569 new_size += p->prev_size;
570 assert (new_size > 0 && new_size < HEAP_MAX_SIZE);
571 if (new_size + (HEAP_MAX_SIZE - prev_heap->size) < pad + MINSIZE + pagesz)
572 break;
573 ar_ptr->system_mem -= heap->size;
574 arena_mem -= heap->size;
575 LIBC_PROBE (memory_heap_free, 2, heap, heap->size);
576 delete_heap (heap);
577 heap = prev_heap;
578 if (!prev_inuse (p)) /* consolidate backward */
579 {
580 p = prev_chunk (p);
581 unlink (ar_ptr, p, bck, fwd);
582 }
583 assert (((unsigned long) ((char *) p + new_size) & (pagesz - 1)) == 0);
584 assert (((char *) p + new_size) == ((char *) heap + heap->size));
585 top (ar_ptr) = top_chunk = p;
586 set_head (top_chunk, new_size | PREV_INUSE);
587 /*check_chunk(ar_ptr, top_chunk);*/
588 }
589
590 /* Uses similar logic for per-thread arenas as the main arena with systrim
591 and _int_free by preserving the top pad and rounding down to the nearest
592 page. */
593 top_size = chunksize (top_chunk);
594 if ((unsigned long)(top_size) <
595 (unsigned long)(mp_.trim_threshold))
596 return 0;
597
598 top_area = top_size - MINSIZE - 1;
599 if (top_area < 0 || (size_t) top_area <= pad)
600 return 0;
601
602 /* Release in pagesize units and round down to the nearest page. */
603 extra = ALIGN_DOWN(top_area - pad, pagesz);
604 if (extra == 0)
605 return 0;
606
607 /* Try to shrink. */
608 if (shrink_heap (heap, extra) != 0)
609 return 0;
610
611 ar_ptr->system_mem -= extra;
612 arena_mem -= extra;
613
614 /* Success. Adjust top accordingly. */
615 set_head (top_chunk, (top_size - extra) | PREV_INUSE);
616 /*check_chunk(ar_ptr, top_chunk);*/
617 return 1;
618}
619
620/* Create a new arena with initial size "size". */
621
622/* If REPLACED_ARENA is not NULL, detach it from this thread. Must be
623 called while free_list_lock is held. */
624static void
625detach_arena (mstate replaced_arena)
626{
627 if (replaced_arena != NULL)
628 {
629 assert (replaced_arena->attached_threads > 0);
630 /* The current implementation only detaches from main_arena in
631 case of allocation failure. This means that it is likely not
632 beneficial to put the arena on free_list even if the
633 reference count reaches zero. */
634 --replaced_arena->attached_threads;
635 }
636}
637
638static mstate
639_int_new_arena (size_t size)
640{
641 mstate a;
642 heap_info *h;
643 char *ptr;
644 unsigned long misalign;
645
646 h = new_heap (size + (sizeof (*h) + sizeof (*a) + MALLOC_ALIGNMENT),
647 mp_.top_pad);
648 if (!h)
649 {
650 /* Maybe size is too large to fit in a single heap. So, just try
651 to create a minimally-sized arena and let _int_malloc() attempt
652 to deal with the large request via mmap_chunk(). */
653 h = new_heap (sizeof (*h) + sizeof (*a) + MALLOC_ALIGNMENT, mp_.top_pad);
654 if (!h)
655 return 0;
656 }
657 a = h->ar_ptr = (mstate) (h + 1);
658 malloc_init_state (a);
659 a->attached_threads = 1;
660 /*a->next = NULL;*/
661 a->system_mem = a->max_system_mem = h->size;
662 arena_mem += h->size;
663
664 /* Set up the top chunk, with proper alignment. */
665 ptr = (char *) (a + 1);
666 misalign = (unsigned long) chunk2mem (ptr) & MALLOC_ALIGN_MASK;
667 if (misalign > 0)
668 ptr += MALLOC_ALIGNMENT - misalign;
669 top (a) = (mchunkptr) ptr;
670 set_head (top (a), (((char *) h + h->size) - ptr) | PREV_INUSE);
671
672 LIBC_PROBE (memory_arena_new, 2, a, size);
673 mstate replaced_arena = thread_arena;
674 thread_arena = a;
675 mutex_init (&a->mutex);
676
677 (void) mutex_lock (&list_lock);
678
679 /* Add the new arena to the global list. */
680 a->next = main_arena.next;
681 /* FIXME: The barrier is an attempt to synchronize with read access
682 in reused_arena, which does not acquire list_lock while
683 traversing the list. */
684 atomic_write_barrier ();
685 main_arena.next = a;
686
687 (void) mutex_unlock (&list_lock);
688
689 (void) mutex_lock (&free_list_lock);
690 detach_arena (replaced_arena);
691 (void) mutex_unlock (&free_list_lock);
692
693 /* Lock this arena. NB: Another thread may have been attached to
694 this arena because the arena is now accessible from the
695 main_arena.next list and could have been picked by reused_arena.
696 This can only happen for the last arena created (before the arena
697 limit is reached). At this point, some arena has to be attached
698 to two threads. We could acquire the arena lock before list_lock
699 to make it less likely that reused_arena picks this new arena,
700 but this could result in a deadlock with
701 __malloc_fork_lock_parent. */
702
703 (void) mutex_lock (&a->mutex);
704
705 return a;
706}
707
708
709/* Remove an arena from free_list. */
710static mstate
711get_free_list (void)
712{
713 mstate replaced_arena = thread_arena;
714 mstate result = free_list;
715 if (result != NULL)
716 {
717 (void) mutex_lock (&free_list_lock);
718 result = free_list;
719 if (result != NULL)
720 {
721 free_list = result->next_free;
722
723 /* The arena will be attached to this thread. */
724 assert (result->attached_threads == 0);
725 result->attached_threads = 1;
726
727 detach_arena (replaced_arena);
728 }
729 (void) mutex_unlock (&free_list_lock);
730
731 if (result != NULL)
732 {
733 LIBC_PROBE (memory_arena_reuse_free_list, 1, result);
734 (void) mutex_lock (&result->mutex);
735 thread_arena = result;
736 }
737 }
738
739 return result;
740}
741
742/* Remove the arena from the free list (if it is present).
743 free_list_lock must have been acquired by the caller. */
744static void
745remove_from_free_list (mstate arena)
746{
747 mstate *previous = &free_list;
748 for (mstate p = free_list; p != NULL; p = p->next_free)
749 {
750 assert (p->attached_threads == 0);
751 if (p == arena)
752 {
753 /* Remove the requested arena from the list. */
754 *previous = p->next_free;
755 break;
756 }
757 else
758 previous = &p->next_free;
759 }
760}
761
762/* Lock and return an arena that can be reused for memory allocation.
763 Avoid AVOID_ARENA as we have already failed to allocate memory in
764 it and it is currently locked. */
765static mstate
766reused_arena (mstate avoid_arena)
767{
768 mstate result;
769 /* FIXME: Access to next_to_use suffers from data races. */
770 static mstate next_to_use;
771 if (next_to_use == NULL)
772 next_to_use = &main_arena;
773
774 /* Iterate over all arenas (including those linked from
775 free_list). */
776 result = next_to_use;
777 do
778 {
779 if (!arena_is_corrupt (result) && !mutex_trylock (&result->mutex))
780 goto out;
781
782 /* FIXME: This is a data race, see _int_new_arena. */
783 result = result->next;
784 }
785 while (result != next_to_use);
786
787 /* Avoid AVOID_ARENA as we have already failed to allocate memory
788 in that arena and it is currently locked. */
789 if (result == avoid_arena)
790 result = result->next;
791
792 /* Make sure that the arena we get is not corrupted. */
793 mstate begin = result;
794 while (arena_is_corrupt (result) || result == avoid_arena)
795 {
796 result = result->next;
797 if (result == begin)
798 /* We looped around the arena list. We could not find any
799 arena that was either not corrupted or not the one we
800 wanted to avoid. */
801 return NULL;
802 }
803
804 /* No arena available without contention. Wait for the next in line. */
805 LIBC_PROBE (memory_arena_reuse_wait, 3, &result->mutex, result, avoid_arena);
806 (void) mutex_lock (&result->mutex);
807
808out:
809 /* Attach the arena to the current thread. */
810 {
811 /* Update the arena thread attachment counters. */
812 mstate replaced_arena = thread_arena;
813 (void) mutex_lock (&free_list_lock);
814 detach_arena (replaced_arena);
815
816 /* We may have picked up an arena on the free list. We need to
817 preserve the invariant that no arena on the free list has a
818 positive attached_threads counter (otherwise,
819 arena_thread_freeres cannot use the counter to determine if the
820 arena needs to be put on the free list). We unconditionally
821 remove the selected arena from the free list. The caller of
822 reused_arena checked the free list and observed it to be empty,
823 so the list is very short. */
824 remove_from_free_list (result);
825
826 ++result->attached_threads;
827
828 (void) mutex_unlock (&free_list_lock);
829 }
830
831 LIBC_PROBE (memory_arena_reuse, 2, result, avoid_arena);
832 thread_arena = result;
833 next_to_use = result->next;
834
835 return result;
836}
837
838static mstate
839internal_function
840arena_get2 (size_t size, mstate avoid_arena)
841{
842 mstate a;
843
844 static size_t narenas_limit;
845
846 a = get_free_list ();
847 if (a == NULL)
848 {
849 /* Nothing immediately available, so generate a new arena. */
850 if (narenas_limit == 0)
851 {
852 if (mp_.arena_max != 0)
853 narenas_limit = mp_.arena_max;
854 else if (narenas > mp_.arena_test)
855 {
856 int n = __get_nprocs ();
857
858 if (n >= 1)
859 narenas_limit = NARENAS_FROM_NCORES (n);
860 else
861 /* We have no information about the system. Assume two
862 cores. */
863 narenas_limit = NARENAS_FROM_NCORES (2);
864 }
865 }
866 repeat:;
867 size_t n = narenas;
868 /* NB: the following depends on the fact that (size_t)0 - 1 is a
869 very large number and that the underflow is OK. If arena_max
870 is set the value of arena_test is irrelevant. If arena_test
871 is set but narenas is not yet larger or equal to arena_test
872 narenas_limit is 0. There is no possibility for narenas to
873 be too big for the test to always fail since there is not
874 enough address space to create that many arenas. */
875 if (__glibc_unlikely (n <= narenas_limit - 1))
876 {
877 if (catomic_compare_and_exchange_bool_acq (&narenas, n + 1, n))
878 goto repeat;
879 a = _int_new_arena (size);
880 if (__glibc_unlikely (a == NULL))
881 catomic_decrement (&narenas);
882 }
883 else
884 a = reused_arena (avoid_arena);
885 }
886 return a;
887}
888
889/* If we don't have the main arena, then maybe the failure is due to running
890 out of mmapped areas, so we can try allocating on the main arena.
891 Otherwise, it is likely that sbrk() has failed and there is still a chance
892 to mmap(), so try one of the other arenas. */
893static mstate
894arena_get_retry (mstate ar_ptr, size_t bytes)
895{
896 LIBC_PROBE (memory_arena_retry, 2, bytes, ar_ptr);
897 if (ar_ptr != &main_arena)
898 {
899 (void) mutex_unlock (&ar_ptr->mutex);
900 /* Don't touch the main arena if it is corrupt. */
901 if (arena_is_corrupt (&main_arena))
902 return NULL;
903
904 ar_ptr = &main_arena;
905 (void) mutex_lock (&ar_ptr->mutex);
906 }
907 else
908 {
909 (void) mutex_unlock (&ar_ptr->mutex);
910 ar_ptr = arena_get2 (bytes, ar_ptr);
911 }
912
913 return ar_ptr;
914}
915
916static void __attribute__ ((section ("__libc_thread_freeres_fn")))
917arena_thread_freeres (void)
918{
919 mstate a = thread_arena;
920 thread_arena = NULL;
921
922 if (a != NULL)
923 {
924 (void) mutex_lock (&free_list_lock);
925 /* If this was the last attached thread for this arena, put the
926 arena on the free list. */
927 assert (a->attached_threads > 0);
928 if (--a->attached_threads == 0)
929 {
930 a->next_free = free_list;
931 free_list = a;
932 }
933 (void) mutex_unlock (&free_list_lock);
934 }
935}
936text_set_element (__libc_thread_subfreeres, arena_thread_freeres);
937
938/*
939 * Local variables:
940 * c-basic-offset: 2
941 * End:
942 */
943