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comparison src/spinlock.c @ 0:83c23a36980d

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author Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp>
date Fri, 26 May 2017 23:11:05 +0900
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children ad1d3b268e2d
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-1:000000000000 0:83c23a36980d
1 // Mutual exclusion spin locks.
2
3 #include "types.h"
4 #include "defs.h"
5 #include "param.h"
6 #include "arm.h"
7 #include "memlayout.h"
8 #include "mmu.h"
9 #include "proc.h"
10 #include "spinlock.h"
11
12 void initlock(struct spinlock *lk, char *name)
13 {
14 lk->name = name;
15 lk->locked = 0;
16 lk->cpu = 0;
17 }
18
19 // For single CPU systems, there is no need for spinlock.
20 // Add the support when multi-processor is supported.
21
22
23 // Acquire the lock.
24 // Loops (spins) until the lock is acquired.
25 // Holding a lock for a long time may cause
26 // other CPUs to waste time spinning to acquire it.
27 void acquire(struct spinlock *lk)
28 {
29 pushcli(); // disable interrupts to avoid deadlock.
30 lk->locked = 1; // set the lock status to make the kernel happy
31
32 #if 0
33 if(holding(lk))
34 panic("acquire");
35
36 // The xchg is atomic.
37 // It also serializes, so that reads after acquire are not
38 // reordered before it.
39 while(xchg(&lk->locked, 1) != 0)
40 ;
41
42 // Record info about lock acquisition for debugging.
43 lk->cpu = cpu;
44 getcallerpcs(get_fp(), lk->pcs);
45
46 #endif
47 }
48
49 // Release the lock.
50 void release(struct spinlock *lk)
51 {
52 #if 0
53 if(!holding(lk))
54 panic("release");
55
56 lk->pcs[0] = 0;
57 lk->cpu = 0;
58
59 // The xchg serializes, so that reads before release are
60 // not reordered after it. The 1996 PentiumPro manual (Volume 3,
61 // 7.2) says reads can be carried out speculatively and in
62 // any order, which implies we need to serialize here.
63 // But the 2007 Intel 64 Architecture Memory Ordering White
64 // Paper says that Intel 64 and IA-32 will not move a load
65 // after a store. So lock->locked = 0 would work here.
66 // The xchg being asm volatile ensures gcc emits it after
67 // the above assignments (and after the critical section).
68 xchg(&lk->locked, 0);
69 #endif
70
71 lk->locked = 0; // set the lock state to keep the kernel happy
72 popcli();
73 }
74
75
76 // Check whether this cpu is holding the lock.
77 int holding(struct spinlock *lock)
78 {
79 return lock->locked; // && lock->cpu == cpus;
80 }
81