futex_wait_requeue_pi (9) - Linux Man Pages
futex_wait_requeue_pi: Wait on uaddr and take uaddr2
futex_wait_requeue_pi - Wait on uaddr and take uaddr2
__useruaddr, unsigned int * flags, u32 val, ktime_t *abs_time, u32 bitset, u32 __useruaddr2); *
- the futex we initially wait on (non-pi)
- futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be the same type, no requeueing from private to shared, etc.
- the expected value of uaddr
- absolute timeout
- 32 bit wakeup bitset set by userspace, defaults to all
- the pi futex we will take prior to returning to user-space
The caller will wait on uaddr and will be requeued by futex_requeue to uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake on uaddr2 and complete the acquisition of the rt_mutex prior to returning to userspace. This ensures the rt_mutex maintains an owner when it has waiters; without one, the pi logic would not know which task to boost/deboost, if there was a need to.
We call schedule in futex_wait_queue_me when we enqueue and return there via the following-- 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue 2) wakeup on uaddr2 after a requeue 3) signal 4) timeout
If 3, cleanup and return -ERESTARTNOINTR.
If 2, we may then block on trying to take the rt_mutex and return via: 5) successful lock 6) signal 7) timeout 8) other lock acquisition failure
If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
Rusty Russell <rusty [at] rustcorp.com.au>