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bfff8b1b | 1 | /* Copyright (C) 2002-2017 Free Software Foundation, Inc. |
76a50749 UD |
2 | This file is part of the GNU C Library. |
3 | Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. | |
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 | |
59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
76a50749 UD |
18 | |
19 | #include <errno.h> | |
20 | #include <stdlib.h> | |
8dea90aa | 21 | #include <fork.h> |
92d83c72 | 22 | #include <atomic.h> |
a2f0363f | 23 | #include <futex-internal.h> |
4e648ea3 UD |
24 | |
25 | ||
76a50749 | 26 | void |
9d46370c | 27 | __unregister_atfork (void *dso_handle) |
76a50749 | 28 | { |
92d83c72 UD |
29 | /* Check whether there is any entry in the list which we have to |
30 | remove. It is likely that this is not the case so don't bother | |
31 | getting the lock. | |
32 | ||
33 | We do not worry about other threads adding entries for this DSO | |
34 | right this moment. If this happens this is a race and we can do | |
35 | whatever we please. The program will crash anyway seen. */ | |
36 | struct fork_handler *runp = __fork_handlers; | |
37 | struct fork_handler *lastp = NULL; | |
38 | ||
39 | while (runp != NULL) | |
40 | if (runp->dso_handle == dso_handle) | |
41 | break; | |
42 | else | |
dfdd294a | 43 | { |
92d83c72 UD |
44 | lastp = runp; |
45 | runp = runp->next; | |
dfdd294a | 46 | } |
76a50749 | 47 | |
92d83c72 UD |
48 | if (runp == NULL) |
49 | /* Nothing to do. */ | |
50 | return; | |
dfdd294a | 51 | |
92d83c72 UD |
52 | /* Get the lock to not conflict with additions or deletions. Note |
53 | that there couldn't have been another thread deleting something. | |
54 | The __unregister_atfork function is only called from the | |
55 | dlclose() code which itself serializes the operations. */ | |
e51deae7 | 56 | lll_lock (__fork_lock, LLL_PRIVATE); |
dfdd294a | 57 | |
92d83c72 UD |
58 | /* We have to create a new list with all the entries we don't remove. */ |
59 | struct deleted_handler | |
60 | { | |
61 | struct fork_handler *handler; | |
62 | struct deleted_handler *next; | |
63 | } *deleted = NULL; | |
64 | ||
65 | /* Remove the entries for the DSO which is unloaded from the list. | |
66 | It's a single linked list so readers are. */ | |
67 | do | |
68 | { | |
ad3371fb | 69 | again: |
92d83c72 UD |
70 | if (runp->dso_handle == dso_handle) |
71 | { | |
72 | if (lastp == NULL) | |
ad3371fb UD |
73 | { |
74 | /* We have to use an atomic operation here because | |
75 | __linkin_atfork also uses one. */ | |
76 | if (catomic_compare_and_exchange_bool_acq (&__fork_handlers, | |
77 | runp->next, runp) | |
78 | != 0) | |
79 | { | |
80 | runp = __fork_handlers; | |
81 | goto again; | |
82 | } | |
83 | } | |
92d83c72 UD |
84 | else |
85 | lastp->next = runp->next; | |
86 | ||
87 | /* We cannot overwrite the ->next element now. Put the deleted | |
88 | entries in a separate list. */ | |
89 | struct deleted_handler *newp = alloca (sizeof (*newp)); | |
90 | newp->handler = runp; | |
91 | newp->next = deleted; | |
92 | deleted = newp; | |
93 | } | |
94 | else | |
95 | lastp = runp; | |
96 | ||
97 | runp = runp->next; | |
98 | } | |
99 | while (runp != NULL); | |
76a50749 UD |
100 | |
101 | /* Release the lock. */ | |
e51deae7 | 102 | lll_unlock (__fork_lock, LLL_PRIVATE); |
92d83c72 UD |
103 | |
104 | /* Walk the list of all entries which have to be deleted. */ | |
105 | while (deleted != NULL) | |
106 | { | |
107 | /* We need to be informed by possible current users. */ | |
108 | deleted->handler->need_signal = 1; | |
109 | /* Make sure this gets written out first. */ | |
110 | atomic_write_barrier (); | |
111 | ||
112 | /* Decrement the reference counter. If it does not reach zero | |
113 | wait for the last user. */ | |
114 | atomic_decrement (&deleted->handler->refcntr); | |
115 | unsigned int val; | |
116 | while ((val = deleted->handler->refcntr) != 0) | |
a2f0363f | 117 | futex_wait_simple (&deleted->handler->refcntr, val, FUTEX_PRIVATE); |
92d83c72 UD |
118 | |
119 | deleted = deleted->next; | |
120 | } | |
76a50749 | 121 | } |