futex_wait_requeue_pi (9)

int futex_wait_requeue_pi(u32 __user * uaddr, unsigned int flags, u32 val, ktime_t * abs_time, u32 bitset, u32 __user * uaddr2);

uaddr

the futex we initially wait on (non-pi)

flags

futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be the same type, no requeueing from private to shared, etc.

val

the expected value of uaddr

abs_time

absolute timeout

bitset

32 bit wakeup bitset set by userspace, defaults to all

uaddr2

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).

If 4 or 7, we cleanup and return with -ETIMEDOUT.

0 - On success; <0 - On error

Rusty Russell <[email protected]>

Author.