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4b393c50 | 1 | /* |
716154c5 BB |
2 | * Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC. |
3 | * Copyright (C) 2007 The Regents of the University of California. | |
4 | * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER). | |
5 | * Written by Brian Behlendorf <behlendorf1@llnl.gov>. | |
715f6251 | 6 | * UCRL-CODE-235197 |
7 | * | |
716154c5 | 8 | * This file is part of the SPL, Solaris Porting Layer. |
3d6af2dd | 9 | * For details, see <http://zfsonlinux.org/>. |
715f6251 | 10 | * |
716154c5 BB |
11 | * The SPL is free software; you can redistribute it and/or modify it |
12 | * under the terms of the GNU General Public License as published by the | |
13 | * Free Software Foundation; either version 2 of the License, or (at your | |
14 | * option) any later version. | |
15 | * | |
16 | * The SPL is distributed in the hope that it will be useful, but WITHOUT | |
715f6251 | 17 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
18 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
19 | * for more details. | |
20 | * | |
21 | * You should have received a copy of the GNU General Public License along | |
716154c5 | 22 | * with the SPL. If not, see <http://www.gnu.org/licenses/>. |
5461eefe | 23 | * |
716154c5 | 24 | * Solaris Porting Layer (SPL) Reader/Writer Lock Implementation. |
4b393c50 | 25 | */ |
715f6251 | 26 | |
f4b37741 | 27 | #include <sys/rwlock.h> |
f1ca4da6 | 28 | |
8e99d66b CF |
29 | #if defined(CONFIG_PREEMPT_RT_FULL) |
30 | ||
31 | #include <linux/rtmutex.h> | |
2d4d81c4 | 32 | #define RT_MUTEX_OWNER_MASKALL 1UL |
8e99d66b CF |
33 | |
34 | static int | |
35 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
36 | { | |
2d4d81c4 | 37 | |
38 | ASSERT((struct task_struct *) | |
39 | ((unsigned long)rwsem->lock.owner & ~RT_MUTEX_OWNER_MASKALL) == | |
40 | current); | |
8e99d66b CF |
41 | |
42 | /* | |
43 | * Under the realtime patch series, rwsem is implemented as a | |
44 | * single mutex held by readers and writers alike. However, | |
45 | * this implementation would prevent a thread from taking a | |
46 | * read lock twice, as the mutex would already be locked on | |
47 | * the second attempt. Therefore the implementation allows a | |
48 | * single thread to take a rwsem as read lock multiple times | |
49 | * tracking that nesting as read_depth counter. | |
50 | */ | |
51 | if (rwsem->read_depth <= 1) { | |
52 | /* | |
53 | * In case, the current thread has not taken the lock | |
54 | * more than once as read lock, we can allow an | |
55 | * upgrade to a write lock. rwsem_rt.h implements | |
56 | * write locks as read_depth == 0. | |
57 | */ | |
58 | rwsem->read_depth = 0; | |
59 | return (1); | |
60 | } | |
61 | return (0); | |
62 | } | |
63 | #elif defined(CONFIG_RWSEM_GENERIC_SPINLOCK) | |
f58040c0 CC |
64 | static int |
65 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
66 | { | |
67 | int ret = 0; | |
68 | unsigned long flags; | |
69 | spl_rwsem_lock_irqsave(&rwsem->wait_lock, flags); | |
70 | if (RWSEM_COUNT(rwsem) == SPL_RWSEM_SINGLE_READER_VALUE && | |
71 | list_empty(&rwsem->wait_list)) { | |
72 | ret = 1; | |
73 | RWSEM_COUNT(rwsem) = SPL_RWSEM_SINGLE_WRITER_VALUE; | |
74 | } | |
75 | spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags); | |
76 | return (ret); | |
77 | } | |
b7c7008b BB |
78 | #elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT) |
79 | static int | |
80 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
81 | { | |
82 | long val; | |
83 | val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE, | |
84 | SPL_RWSEM_SINGLE_WRITER_VALUE); | |
85 | return (val == SPL_RWSEM_SINGLE_READER_VALUE); | |
86 | } | |
f58040c0 CC |
87 | #else |
88 | static int | |
89 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
90 | { | |
5461eefe | 91 | typeof(rwsem->count) val; |
f58040c0 CC |
92 | val = cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE, |
93 | SPL_RWSEM_SINGLE_WRITER_VALUE); | |
94 | return (val == SPL_RWSEM_SINGLE_READER_VALUE); | |
95 | } | |
96 | #endif | |
97 | ||
98 | int | |
99 | rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
100 | { | |
101 | if (__rwsem_tryupgrade(rwsem)) { | |
102 | rwsem_release(&rwsem->dep_map, 1, _RET_IP_); | |
103 | rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); | |
104 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER | |
105 | rwsem->owner = current; | |
106 | #endif | |
107 | return (1); | |
108 | } | |
109 | return (0); | |
110 | } | |
111 | EXPORT_SYMBOL(rwsem_tryupgrade); | |
112 | ||
d28db80f BB |
113 | int spl_rw_init(void) { return 0; } |
114 | void spl_rw_fini(void) { } |