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1 | /*****************************************************************************\ |
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/>. |
34ee731f | 23 | * |
716154c5 BB |
24 | * Solaris Porting Layer (SPL) Reader/Writer Lock Implementation. |
25 | \*****************************************************************************/ | |
715f6251 | 26 | |
f4b37741 | 27 | #include <sys/rwlock.h> |
f1ca4da6 | 28 | |
ec06701b AX |
29 | #if defined(CONFIG_PREEMPT_RT_FULL) |
30 | ||
31 | #include <linux/rtmutex.h> | |
32 | #define RT_MUTEX_OWNER_MASKALL 1UL | |
33 | ||
34 | static int | |
35 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
36 | { | |
b97c7791 MZ |
37 | #if defined(READER_BIAS) && defined(WRITER_BIAS) |
38 | /* | |
39 | * After the 4.9.20-rt16 kernel the realtime patch series lifted the | |
40 | * single reader restriction. While this could be accommodated by | |
41 | * adding additional compatibility code assume the rwsem can never | |
42 | * be upgraded. All caller must already cleanly handle this case. | |
43 | */ | |
44 | return (0); | |
45 | #else | |
ec06701b AX |
46 | ASSERT((struct task_struct *) |
47 | ((unsigned long)rwsem->lock.owner & ~RT_MUTEX_OWNER_MASKALL) == | |
48 | current); | |
49 | ||
50 | /* | |
b97c7791 MZ |
51 | * Prior to 4.9.20-rt16 kernel the realtime patch series, rwsem is |
52 | * implemented as a single mutex held by readers and writers alike. | |
53 | * However, this implementation would prevent a thread from taking | |
54 | * a read lock twice, as the mutex would already be locked on | |
ec06701b AX |
55 | * the second attempt. Therefore the implementation allows a |
56 | * single thread to take a rwsem as read lock multiple times | |
57 | * tracking that nesting as read_depth counter. | |
58 | */ | |
59 | if (rwsem->read_depth <= 1) { | |
60 | /* | |
61 | * In case, the current thread has not taken the lock | |
62 | * more than once as read lock, we can allow an | |
63 | * upgrade to a write lock. rwsem_rt.h implements | |
64 | * write locks as read_depth == 0. | |
65 | */ | |
66 | rwsem->read_depth = 0; | |
67 | return (1); | |
68 | } | |
69 | return (0); | |
b97c7791 | 70 | #endif |
ec06701b AX |
71 | } |
72 | #elif defined(CONFIG_RWSEM_GENERIC_SPINLOCK) | |
0f836a62 AX |
73 | static int |
74 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
e8b31e84 | 75 | { |
0f836a62 AX |
76 | int ret = 0; |
77 | unsigned long flags; | |
78 | spl_rwsem_lock_irqsave(&rwsem->wait_lock, flags); | |
79 | if (RWSEM_COUNT(rwsem) == SPL_RWSEM_SINGLE_READER_VALUE && | |
80 | list_empty(&rwsem->wait_list)) { | |
81 | ret = 1; | |
82 | RWSEM_COUNT(rwsem) = SPL_RWSEM_SINGLE_WRITER_VALUE; | |
83 | } | |
84 | spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags); | |
85 | return (ret); | |
e8b31e84 | 86 | } |
0f836a62 AX |
87 | #elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT) |
88 | static int | |
89 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
e8b31e84 | 90 | { |
0f836a62 AX |
91 | long val; |
92 | val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE, | |
93 | SPL_RWSEM_SINGLE_WRITER_VALUE); | |
94 | return (val == SPL_RWSEM_SINGLE_READER_VALUE); | |
e8b31e84 | 95 | } |
0f836a62 AX |
96 | #else |
97 | static int | |
98 | __rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
e8b31e84 | 99 | { |
34ee731f | 100 | typeof(rwsem->count) val; |
0f836a62 AX |
101 | val = cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE, |
102 | SPL_RWSEM_SINGLE_WRITER_VALUE); | |
103 | return (val == SPL_RWSEM_SINGLE_READER_VALUE); | |
f1ca4da6 | 104 | } |
0f836a62 | 105 | #endif |
79f92663 | 106 | |
0f836a62 AX |
107 | int |
108 | rwsem_tryupgrade(struct rw_semaphore *rwsem) | |
109 | { | |
110 | if (__rwsem_tryupgrade(rwsem)) { | |
111 | rwsem_release(&rwsem->dep_map, 1, _RET_IP_); | |
112 | rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); | |
113 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER | |
114 | rwsem->owner = current; | |
ed61a7d0 | 115 | #endif |
0f836a62 AX |
116 | return (1); |
117 | } | |
118 | return (0); | |
119 | } | |
120 | EXPORT_SYMBOL(rwsem_tryupgrade); | |
d28db80f BB |
121 | |
122 | int spl_rw_init(void) { return 0; } | |
123 | void spl_rw_fini(void) { } |