summaryrefslogtreecommitdiff
path: root/include/linux/futex.h
blob: 55fff96ae85914c7d6138428a471bb8ef4a2a369 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
#ifndef _LINUX_FUTEX_H
#define _LINUX_FUTEX_H

#include <linux/sched.h>

/* Second argument to futex syscall */


#define FUTEX_WAIT		0
#define FUTEX_WAKE		1
#define FUTEX_FD		2
#define FUTEX_REQUEUE		3
#define FUTEX_CMP_REQUEUE	4
#define FUTEX_WAKE_OP		5

/*
 * Support for robust futexes: the kernel cleans up held futexes at
 * thread exit time.
 */

/*
 * Per-lock list entry - embedded in user-space locks, somewhere close
 * to the futex field. (Note: user-space uses a double-linked list to
 * achieve O(1) list add and remove, but the kernel only needs to know
 * about the forward link)
 *
 * NOTE: this structure is part of the syscall ABI, and must not be
 * changed.
 */
struct robust_list {
	struct robust_list __user *next;
};

/*
 * Per-thread list head:
 *
 * NOTE: this structure is part of the syscall ABI, and must only be
 * changed if the change is first communicated with the glibc folks.
 * (When an incompatible change is done, we'll increase the structure
 *  size, which glibc will detect)
 */
struct robust_list_head {
	/*
	 * The head of the list. Points back to itself if empty:
	 */
	struct robust_list list;

	/*
	 * This relative offset is set by user-space, it gives the kernel
	 * the relative position of the futex field to examine. This way
	 * we keep userspace flexible, to freely shape its data-structure,
	 * without hardcoding any particular offset into the kernel:
	 */
	long futex_offset;

	/*
	 * The death of the thread may race with userspace setting
	 * up a lock's links. So to handle this race, userspace first
	 * sets this field to the address of the to-be-taken lock,
	 * then does the lock acquire, and then adds itself to the
	 * list, and then clears this field. Hence the kernel will
	 * always have full knowledge of all locks that the thread
	 * _might_ have taken. We check the owner TID in any case,
	 * so only truly owned locks will be handled.
	 */
	struct robust_list __user *list_op_pending;
};

/*
 * Are there any waiters for this robust futex:
 */
#define FUTEX_WAITERS		0x80000000

/*
 * The kernel signals via this bit that a thread holding a futex
 * has exited without unlocking the futex. The kernel also does
 * a FUTEX_WAKE on such futexes, after setting the bit, to wake
 * up any possible waiters:
 */
#define FUTEX_OWNER_DIED	0x40000000

/*
 * Reserved bit:
 */
#define FUTEX_OWNER_PENDING	0x20000000

/*
 * The rest of the robust-futex field is for the TID:
 */
#define FUTEX_TID_MASK		0x1fffffff

/*
 * A limit of one million locks held per thread (!) ought to be enough
 * for some time. This also protects against a deliberately circular
 * list. Not worth introducing an rlimit for this:
 */
#define ROBUST_LIST_LIMIT	1048576

long do_futex(unsigned long uaddr, int op, int val,
		unsigned long timeout, unsigned long uaddr2, int val2,
		int val3);

extern int handle_futex_death(u32 __user *uaddr, struct task_struct *curr);

#ifdef CONFIG_FUTEX
extern void exit_robust_list(struct task_struct *curr);
#else
static inline void exit_robust_list(struct task_struct *curr)
{
}
#endif

#define FUTEX_OP_SET		0	/* *(int *)UADDR2 = OPARG; */
#define FUTEX_OP_ADD		1	/* *(int *)UADDR2 += OPARG; */
#define FUTEX_OP_OR		2	/* *(int *)UADDR2 |= OPARG; */
#define FUTEX_OP_ANDN		3	/* *(int *)UADDR2 &= ~OPARG; */
#define FUTEX_OP_XOR		4	/* *(int *)UADDR2 ^= OPARG; */

#define FUTEX_OP_OPARG_SHIFT	8	/* Use (1 << OPARG) instead of OPARG.  */

#define FUTEX_OP_CMP_EQ		0	/* if (oldval == CMPARG) wake */
#define FUTEX_OP_CMP_NE		1	/* if (oldval != CMPARG) wake */
#define FUTEX_OP_CMP_LT		2	/* if (oldval < CMPARG) wake */
#define FUTEX_OP_CMP_LE		3	/* if (oldval <= CMPARG) wake */
#define FUTEX_OP_CMP_GT		4	/* if (oldval > CMPARG) wake */
#define FUTEX_OP_CMP_GE		5	/* if (oldval >= CMPARG) wake */

/* FUTEX_WAKE_OP will perform atomically
   int oldval = *(int *)UADDR2;
   *(int *)UADDR2 = oldval OP OPARG;
   if (oldval CMP CMPARG)
     wake UADDR2;  */

#define FUTEX_OP(op, oparg, cmp, cmparg) \
  (((op & 0xf) << 28) | ((cmp & 0xf) << 24)		\
   | ((oparg & 0xfff) << 12) | (cmparg & 0xfff))

#endif