1/* Set current priority ceiling of pthread_mutex_t.
2 Copyright (C) 2006-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Jakub Jelinek <jakub@redhat.com>, 2006.
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
8 License as published by the Free Software Foundation; either
9 version 2.1 of the 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; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <stdbool.h>
21#include <errno.h>
22#include <pthreadP.h>
23#include <atomic.h>
24
25
26int
27pthread_mutex_setprioceiling (pthread_mutex_t *mutex, int prioceiling,
28 int *old_ceiling)
29{
30 /* See concurrency notes regarding __kind in struct __pthread_mutex_s
31 in sysdeps/nptl/bits/thread-shared-types.h. */
32 if ((atomic_load_relaxed (&(mutex->__data.__kind))
33 & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0)
34 return EINVAL;
35
36 /* See __init_sched_fifo_prio. */
37 if (atomic_load_relaxed (&__sched_fifo_min_prio) == -1
38 || atomic_load_relaxed (&__sched_fifo_max_prio) == -1)
39 __init_sched_fifo_prio ();
40
41 if (__glibc_unlikely (prioceiling
42 < atomic_load_relaxed (&__sched_fifo_min_prio))
43 || __glibc_unlikely (prioceiling
44 > atomic_load_relaxed (&__sched_fifo_max_prio))
45 || __glibc_unlikely ((prioceiling
46 & (PTHREAD_MUTEXATTR_PRIO_CEILING_MASK
47 >> PTHREAD_MUTEXATTR_PRIO_CEILING_SHIFT))
48 != prioceiling))
49 return EINVAL;
50
51 /* Check whether we already hold the mutex. */
52 bool locked = false;
53 int kind = PTHREAD_MUTEX_TYPE (mutex);
54 if (mutex->__data.__owner == THREAD_GETMEM (THREAD_SELF, tid))
55 {
56 if (kind == PTHREAD_MUTEX_PP_ERRORCHECK_NP)
57 return EDEADLK;
58
59 if (kind == PTHREAD_MUTEX_PP_RECURSIVE_NP)
60 locked = true;
61 }
62
63 int oldval = mutex->__data.__lock;
64 if (! locked)
65 do
66 {
67 /* Need to lock the mutex, but without obeying the priority
68 protect protocol. */
69 int ceilval = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK);
70
71 oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
72 ceilval | 1, ceilval);
73 if (oldval == ceilval)
74 break;
75
76 do
77 {
78 oldval
79 = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
80 ceilval | 2,
81 ceilval | 1);
82
83 if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
84 break;
85
86 if (oldval != ceilval)
87 lll_futex_wait (&mutex->__data.__lock, ceilval | 2,
88 PTHREAD_MUTEX_PSHARED (mutex));
89 }
90 while (atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
91 ceilval | 2, ceilval)
92 != ceilval);
93
94 if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
95 continue;
96 }
97 while (0);
98
99 int oldprio = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
100 >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
101 if (locked)
102 {
103 int ret = __pthread_tpp_change_priority (oldprio, prioceiling);
104 if (ret)
105 return ret;
106 }
107
108 if (old_ceiling != NULL)
109 *old_ceiling = oldprio;
110
111 int newlock = 0;
112 if (locked)
113 newlock = (mutex->__data.__lock & ~PTHREAD_MUTEX_PRIO_CEILING_MASK);
114 mutex->__data.__lock = newlock
115 | (prioceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT);
116 atomic_full_barrier ();
117
118 lll_futex_wake (&mutex->__data.__lock, INT_MAX,
119 PTHREAD_MUTEX_PSHARED (mutex));
120
121 return 0;
122}
123