4 #include <linux/sched.h>
6 /* Second argument to futex syscall */
12 #define FUTEX_REQUEUE 3
13 #define FUTEX_CMP_REQUEUE 4
14 #define FUTEX_WAKE_OP 5
17 * Support for robust futexes: the kernel cleans up held futexes at
22 * Per-lock list entry - embedded in user-space locks, somewhere close
23 * to the futex field. (Note: user-space uses a double-linked list to
24 * achieve O(1) list add and remove, but the kernel only needs to know
25 * about the forward link)
27 * NOTE: this structure is part of the syscall ABI, and must not be
31 struct robust_list __user *next;
35 * Per-thread list head:
37 * NOTE: this structure is part of the syscall ABI, and must only be
38 * changed if the change is first communicated with the glibc folks.
39 * (When an incompatible change is done, we'll increase the structure
40 * size, which glibc will detect)
42 struct robust_list_head {
44 * The head of the list. Points back to itself if empty:
46 struct robust_list list;
49 * This relative offset is set by user-space, it gives the kernel
50 * the relative position of the futex field to examine. This way
51 * we keep userspace flexible, to freely shape its data-structure,
52 * without hardcoding any particular offset into the kernel:
57 * The death of the thread may race with userspace setting
58 * up a lock's links. So to handle this race, userspace first
59 * sets this field to the address of the to-be-taken lock,
60 * then does the lock acquire, and then adds itself to the
61 * list, and then clears this field. Hence the kernel will
62 * always have full knowledge of all locks that the thread
63 * _might_ have taken. We check the owner TID in any case,
64 * so only truly owned locks will be handled.
66 struct robust_list __user *list_op_pending;
70 * Are there any waiters for this robust futex:
72 #define FUTEX_WAITERS 0x80000000
75 * The kernel signals via this bit that a thread holding a futex
76 * has exited without unlocking the futex. The kernel also does
77 * a FUTEX_WAKE on such futexes, after setting the bit, to wake
78 * up any possible waiters:
80 #define FUTEX_OWNER_DIED 0x40000000
85 #define FUTEX_OWNER_PENDING 0x20000000
88 * The rest of the robust-futex field is for the TID:
90 #define FUTEX_TID_MASK 0x1fffffff
93 * A limit of one million locks held per thread (!) ought to be enough
94 * for some time. This also protects against a deliberately circular
95 * list. Not worth introducing an rlimit for this:
97 #define ROBUST_LIST_LIMIT 1048576
99 long do_futex(unsigned long uaddr, int op, int val,
100 unsigned long timeout, unsigned long uaddr2, int val2,
103 extern int handle_futex_death(unsigned int *uaddr, struct task_struct *curr);
106 extern void exit_robust_list(struct task_struct *curr);
108 static inline void exit_robust_list(struct task_struct *curr)
113 #define FUTEX_OP_SET 0 /* *(int *)UADDR2 = OPARG; */
114 #define FUTEX_OP_ADD 1 /* *(int *)UADDR2 += OPARG; */
115 #define FUTEX_OP_OR 2 /* *(int *)UADDR2 |= OPARG; */
116 #define FUTEX_OP_ANDN 3 /* *(int *)UADDR2 &= ~OPARG; */
117 #define FUTEX_OP_XOR 4 /* *(int *)UADDR2 ^= OPARG; */
119 #define FUTEX_OP_OPARG_SHIFT 8 /* Use (1 << OPARG) instead of OPARG. */
121 #define FUTEX_OP_CMP_EQ 0 /* if (oldval == CMPARG) wake */
122 #define FUTEX_OP_CMP_NE 1 /* if (oldval != CMPARG) wake */
123 #define FUTEX_OP_CMP_LT 2 /* if (oldval < CMPARG) wake */
124 #define FUTEX_OP_CMP_LE 3 /* if (oldval <= CMPARG) wake */
125 #define FUTEX_OP_CMP_GT 4 /* if (oldval > CMPARG) wake */
126 #define FUTEX_OP_CMP_GE 5 /* if (oldval >= CMPARG) wake */
128 /* FUTEX_WAKE_OP will perform atomically
129 int oldval = *(int *)UADDR2;
130 *(int *)UADDR2 = oldval OP OPARG;
131 if (oldval CMP CMPARG)
134 #define FUTEX_OP(op, oparg, cmp, cmparg) \
135 (((op & 0xf) << 28) | ((cmp & 0xf) << 24) \
136 | ((oparg & 0xfff) << 12) | (cmparg & 0xfff))