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1 | /* |
2 | * lib/kernel_lock.c |
3 | * |
4 | * This is the traditional BKL - big kernel lock. Largely |
5 | * relegated to obsolescence, but used by various less |
6 | * important (or lazy) subsystems. |
7 | */ |
8 | #include <linux/module.h> |
9 | #include <linux/kallsyms.h> |
10 | #include <linux/semaphore.h> |
11 | #include <linux/smp_lock.h> |
12 | |
13 | #define CREATE_TRACE_POINTS |
14 | #include <trace/events/bkl.h> |
15 | |
16 | /* |
17 | * The 'big kernel lock' |
18 | * |
19 | * This spinlock is taken and released recursively by lock_kernel() |
20 | * and unlock_kernel(). It is transparently dropped and reacquired |
21 | * over schedule(). It is used to protect legacy code that hasn't |
22 | * been migrated to a proper locking design yet. |
23 | * |
24 | * Don't use in new code. |
25 | */ |
26 | static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(kernel_flag); |
27 | |
28 | |
29 | /* |
30 | * Acquire/release the underlying lock from the scheduler. |
31 | * |
32 | * This is called with preemption disabled, and should |
33 | * return an error value if it cannot get the lock and |
34 | * TIF_NEED_RESCHED gets set. |
35 | * |
36 | * If it successfully gets the lock, it should increment |
37 | * the preemption count like any spinlock does. |
38 | * |
39 | * (This works on UP too - do_raw_spin_trylock will never |
40 | * return false in that case) |
41 | */ |
42 | int __lockfunc __reacquire_kernel_lock(void) |
43 | { |
44 | while (!do_raw_spin_trylock(&kernel_flag)) { |
45 | if (need_resched()) |
46 | return -EAGAIN; |
47 | cpu_relax(); |
48 | } |
49 | preempt_disable(); |
50 | return 0; |
51 | } |
52 | |
53 | void __lockfunc __release_kernel_lock(void) |
54 | { |
55 | do_raw_spin_unlock(&kernel_flag); |
56 | preempt_enable_no_resched(); |
57 | } |
58 | |
59 | /* |
60 | * These are the BKL spinlocks - we try to be polite about preemption. |
61 | * If SMP is not on (ie UP preemption), this all goes away because the |
62 | * do_raw_spin_trylock() will always succeed. |
63 | */ |
64 | #ifdef CONFIG_PREEMPT |
65 | static inline void __lock_kernel(void) |
66 | { |
67 | preempt_disable(); |
68 | if (unlikely(!do_raw_spin_trylock(&kernel_flag))) { |
69 | /* |
70 | * If preemption was disabled even before this |
71 | * was called, there's nothing we can be polite |
72 | * about - just spin. |
73 | */ |
74 | if (preempt_count() > 1) { |
75 | do_raw_spin_lock(&kernel_flag); |
76 | return; |
77 | } |
78 | |
79 | /* |
80 | * Otherwise, let's wait for the kernel lock |
81 | * with preemption enabled.. |
82 | */ |
83 | do { |
84 | preempt_enable(); |
85 | while (raw_spin_is_locked(&kernel_flag)) |
86 | cpu_relax(); |
87 | preempt_disable(); |
88 | } while (!do_raw_spin_trylock(&kernel_flag)); |
89 | } |
90 | } |
91 | |
92 | #else |
93 | |
94 | /* |
95 | * Non-preemption case - just get the spinlock |
96 | */ |
97 | static inline void __lock_kernel(void) |
98 | { |
99 | do_raw_spin_lock(&kernel_flag); |
100 | } |
101 | #endif |
102 | |
103 | static inline void __unlock_kernel(void) |
104 | { |
105 | /* |
106 | * the BKL is not covered by lockdep, so we open-code the |
107 | * unlocking sequence (and thus avoid the dep-chain ops): |
108 | */ |
109 | do_raw_spin_unlock(&kernel_flag); |
110 | preempt_enable(); |
111 | } |
112 | |
113 | /* |
114 | * Getting the big kernel lock. |
115 | * |
116 | * This cannot happen asynchronously, so we only need to |
117 | * worry about other CPU's. |
118 | */ |
119 | void __lockfunc _lock_kernel(const char *func, const char *file, int line) |
120 | { |
121 | int depth = current->lock_depth + 1; |
122 | |
123 | trace_lock_kernel(func, file, line); |
124 | |
125 | if (likely(!depth)) { |
126 | might_sleep(); |
127 | __lock_kernel(); |
128 | } |
129 | current->lock_depth = depth; |
130 | } |
131 | |
132 | void __lockfunc _unlock_kernel(const char *func, const char *file, int line) |
133 | { |
134 | BUG_ON(current->lock_depth < 0); |
135 | if (likely(--current->lock_depth < 0)) |
136 | __unlock_kernel(); |
137 | |
138 | trace_unlock_kernel(func, file, line); |
139 | } |
140 | |
141 | EXPORT_SYMBOL(_lock_kernel); |
142 | EXPORT_SYMBOL(_unlock_kernel); |
143 | |
144 |
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