1 /* System specific fork hooks. Linux version.
2 Copyright (C) 2021-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #ifndef _FORK_H
20 #define _FORK_H
21
22 #include <assert.h>
23 #include <kernel-posix-timers.h>
24 #include <ldsodefs.h>
25 #include <list.h>
26 #include <mqueue.h>
27 #include <pthreadP.h>
28 #include <sysdep.h>
29
30 static inline void
31 fork_system_setup (void)
32 {
33 /* See __pthread_once. */
34 __fork_generation += __PTHREAD_ONCE_FORK_GEN_INCR;
35 }
36
37 static void
38 fork_system_setup_after_fork (void)
39 {
40 /* There is one thread running. */
41 __nptl_nthreads = 1;
42
43 /* Initialize thread library locks. */
44 GL (dl_stack_cache_lock) = LLL_LOCK_INITIALIZER;
45 __default_pthread_attr_lock = LLL_LOCK_INITIALIZER;
46
47 call_function_static_weak (__mq_notify_fork_subprocess);
48 call_function_static_weak (__timer_fork_subprocess);
49 }
50
51 /* In case of a fork() call the memory allocation in the child will be
52 the same but only one thread is running. All stacks except that of
53 the one running thread are not used anymore. We have to recycle
54 them. */
55 static void
56 reclaim_stacks (void)
57 {
58 struct pthread *self = (struct pthread *) THREAD_SELF;
59
60 /* No locking necessary. The caller is the only stack in use. But
61 we have to be aware that we might have interrupted a list
62 operation. */
63
64 if (GL (dl_in_flight_stack) != 0)
65 {
66 bool add_p = GL (dl_in_flight_stack) & 1;
67 list_t *elem = (list_t *) (GL (dl_in_flight_stack) & ~(uintptr_t) 1);
68
69 if (add_p)
70 {
71 /* We always add at the beginning of the list. So in this case we
72 only need to check the beginning of these lists to see if the
73 pointers at the head of the list are inconsistent. */
74 list_t *l = NULL;
75
76 if (GL (dl_stack_used).next->prev != &GL (dl_stack_used))
77 l = &GL (dl_stack_used);
78 else if (GL (dl_stack_cache).next->prev != &GL (dl_stack_cache))
79 l = &GL (dl_stack_cache);
80
81 if (l != NULL)
82 {
83 assert (l->next->prev == elem);
84 elem->next = l->next;
85 elem->prev = l;
86 l->next = elem;
87 }
88 }
89 else
90 {
91 /* We can simply always replay the delete operation. */
92 elem->next->prev = elem->prev;
93 elem->prev->next = elem->next;
94 }
95
96 GL (dl_in_flight_stack) = 0;
97 }
98
99 /* Mark all stacks except the still running one as free. */
100 list_t *runp;
101 list_for_each (runp, &GL (dl_stack_used))
102 {
103 struct pthread *curp = list_entry (runp, struct pthread, list);
104 if (curp != self)
105 {
106 /* This marks the stack as free. */
107 curp->tid = 0;
108
109 /* Account for the size of the stack. */
110 GL (dl_stack_cache_actsize) += curp->stackblock_size;
111
112 if (curp->specific_used)
113 {
114 /* Clear the thread-specific data. */
115 memset (curp->specific_1stblock, '\0',
116 sizeof (curp->specific_1stblock));
117
118 curp->specific_used = false;
119
120 for (size_t cnt = 1; cnt < PTHREAD_KEY_1STLEVEL_SIZE; ++cnt)
121 if (curp->specific[cnt] != NULL)
122 {
123 memset (curp->specific[cnt], '\0',
124 sizeof (curp->specific_1stblock));
125
126 /* We have allocated the block which we do not
127 free here so re-set the bit. */
128 curp->specific_used = true;
129 }
130 }
131 }
132 }
133
134 /* Add the stack of all running threads to the cache. */
135 list_splice (&GL (dl_stack_used), &GL (dl_stack_cache));
136
137 /* Remove the entry for the current thread to from the cache list
138 and add it to the list of running threads. Which of the two
139 lists is decided by the user_stack flag. */
140 list_del (&self->list);
141
142 /* Re-initialize the lists for all the threads. */
143 INIT_LIST_HEAD (&GL (dl_stack_used));
144 INIT_LIST_HEAD (&GL (dl_stack_user));
145
146 if (__glibc_unlikely (THREAD_GETMEM (self, user_stack)))
147 list_add (&self->list, &GL (dl_stack_user));
148 else
149 list_add (&self->list, &GL (dl_stack_used));
150 }
151
152
153 #endif