| 1 |
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| 2 | #ifndef _VDSO_FUTEX_H
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| 3 | #define _VDSO_FUTEX_H
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| 4 |
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| 5 | #include <uapi/linux/types.h>
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| 6 |
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| 7 | |
| 8 | * __vdso_futex_robust_list64_try_unlock - Try to unlock an uncontended robust futex
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| 9 | * with a 64-bit pending op pointer
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| 10 | * @lock: Pointer to the futex lock object
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| 11 | * @tid: The TID of the calling task
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| 12 | * @pop: Pointer to the task's robust_list_head::list_pending_op
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| 13 | *
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| 14 | * Return: The content of *@lock. On success this is the same as @tid.
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| 15 | *
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| 16 | * The function implements:
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| 17 | * if (atomic_try_cmpxchg(lock, &tid, 0))
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| 18 | * *op = NULL;
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| 19 | * return tid;
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| 20 | *
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| 21 | * There is a race between a successful unlock and clearing the pending op
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| 22 | * pointer in the robust list head. If the calling task is interrupted in the
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| 23 | * race window and has to handle a (fatal) signal on return to user space then
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| 24 | * the kernel handles the clearing of @pending_op before attempting to deliver
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| 25 | * the signal. That ensures that a task cannot exit with a potentially invalid
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| 26 | * pending op pointer.
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| 27 | *
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| 28 | * User space uses it in the following way:
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| 29 | *
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| 30 | * if (__vdso_futex_robust_list64_try_unlock(lock, tid, &pending_op) != tid)
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| 31 | * err = sys_futex($OP | FUTEX_ROBUST_UNLOCK,....);
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| 32 | *
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| 33 | * If the unlock attempt fails due to the FUTEX_WAITERS bit set in the lock,
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| 34 | * then the syscall does the unlock, clears the pending op pointer and wakes the
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| 35 | * requested number of waiters.
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| 36 |
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| 37 | __u32 __vdso_futex_robust_list64_try_unlock(__u32 *lock, __u32 tid, __u64 *pop);
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| 38 |
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| 39 | |
| 40 | * __vdso_futex_robust_list32_try_unlock - Try to unlock an uncontended robust futex
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| 41 | * with a 32-bit pending op pointer
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| 42 | * @lock: Pointer to the futex lock object
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| 43 | * @tid: The TID of the calling task
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| 44 | * @pop: Pointer to the task's robust_list_head::list_pending_op
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| 45 | *
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| 46 | * Return: The content of *@lock. On success this is the same as @tid.
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| 47 | *
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| 48 | * Same as __vdso_futex_robust_list64_try_unlock() just with a 32-bit @pop pointer.
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| 49 |
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| 50 | __u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop);
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| 51 |
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| 52 | #endif
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