Commit | Line | Data |
---|---|---|
f038cc13 KO |
1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef __LINUX_SEQLOCK_TYPES_H | |
3 | #define __LINUX_SEQLOCK_TYPES_H | |
4 | ||
5 | #include <linux/lockdep_types.h> | |
6 | #include <linux/mutex_types.h> | |
7 | #include <linux/spinlock_types.h> | |
8 | ||
9 | /* | |
10 | * Sequence counters (seqcount_t) | |
11 | * | |
12 | * This is the raw counting mechanism, without any writer protection. | |
13 | * | |
14 | * Write side critical sections must be serialized and non-preemptible. | |
15 | * | |
16 | * If readers can be invoked from hardirq or softirq contexts, | |
17 | * interrupts or bottom halves must also be respectively disabled before | |
18 | * entering the write section. | |
19 | * | |
20 | * This mechanism can't be used if the protected data contains pointers, | |
21 | * as the writer can invalidate a pointer that a reader is following. | |
22 | * | |
23 | * If the write serialization mechanism is one of the common kernel | |
24 | * locking primitives, use a sequence counter with associated lock | |
25 | * (seqcount_LOCKNAME_t) instead. | |
26 | * | |
27 | * If it's desired to automatically handle the sequence counter writer | |
28 | * serialization and non-preemptibility requirements, use a sequential | |
29 | * lock (seqlock_t) instead. | |
30 | * | |
31 | * See Documentation/locking/seqlock.rst | |
32 | */ | |
33 | typedef struct seqcount { | |
34 | unsigned sequence; | |
35 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
36 | struct lockdep_map dep_map; | |
37 | #endif | |
38 | } seqcount_t; | |
39 | ||
40 | /* | |
41 | * For PREEMPT_RT, seqcount_LOCKNAME_t write side critical sections cannot | |
42 | * disable preemption. It can lead to higher latencies, and the write side | |
43 | * sections will not be able to acquire locks which become sleeping locks | |
44 | * (e.g. spinlock_t). | |
45 | * | |
46 | * To remain preemptible while avoiding a possible livelock caused by the | |
47 | * reader preempting the writer, use a different technique: let the reader | |
48 | * detect if a seqcount_LOCKNAME_t writer is in progress. If that is the | |
49 | * case, acquire then release the associated LOCKNAME writer serialization | |
50 | * lock. This will allow any possibly-preempted writer to make progress | |
51 | * until the end of its writer serialization lock critical section. | |
52 | * | |
53 | * This lock-unlock technique must be implemented for all of PREEMPT_RT | |
54 | * sleeping locks. See Documentation/locking/locktypes.rst | |
55 | */ | |
56 | #if defined(CONFIG_LOCKDEP) || defined(CONFIG_PREEMPT_RT) | |
57 | #define __SEQ_LOCK(expr) expr | |
58 | #else | |
59 | #define __SEQ_LOCK(expr) | |
60 | #endif | |
61 | ||
62 | #define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockbase) \ | |
63 | typedef struct seqcount_##lockname { \ | |
64 | seqcount_t seqcount; \ | |
65 | __SEQ_LOCK(locktype *lock); \ | |
66 | } seqcount_##lockname##_t; | |
67 | ||
68 | SEQCOUNT_LOCKNAME(raw_spinlock, raw_spinlock_t, false, raw_spin) | |
69 | SEQCOUNT_LOCKNAME(spinlock, spinlock_t, __SEQ_RT, spin) | |
70 | SEQCOUNT_LOCKNAME(rwlock, rwlock_t, __SEQ_RT, read) | |
71 | SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex) | |
72 | #undef SEQCOUNT_LOCKNAME | |
73 | ||
74 | /* | |
75 | * Sequential locks (seqlock_t) | |
76 | * | |
77 | * Sequence counters with an embedded spinlock for writer serialization | |
78 | * and non-preemptibility. | |
79 | * | |
80 | * For more info, see: | |
81 | * - Comments on top of seqcount_t | |
82 | * - Documentation/locking/seqlock.rst | |
83 | */ | |
84 | typedef struct { | |
85 | /* | |
86 | * Make sure that readers don't starve writers on PREEMPT_RT: use | |
87 | * seqcount_spinlock_t instead of seqcount_t. Check __SEQ_LOCK(). | |
88 | */ | |
89 | seqcount_spinlock_t seqcount; | |
90 | spinlock_t lock; | |
91 | } seqlock_t; | |
92 | ||
93 | #endif /* __LINUX_SEQLOCK_TYPES_H */ |