'\" t
.\"     Title: futex_wait_requeue_pi
.\"    Author: 
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: July 2017
.\"    Manual: Futex API reference
.\"    Source: Kernel Hackers Manual 4.12.2
.\"  Language: English
.\"
.TH "FUTEX_WAIT_REQUEUE_P" "9" "July 2017" "Kernel Hackers Manual 4\&.12\&" "Futex API reference"
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.SH "NAME"
futex_wait_requeue_pi \- Wait on uaddr and take uaddr2
.SH "SYNOPSIS"
.HP \w'int\ futex_wait_requeue_pi('u
.BI "int futex_wait_requeue_pi(u32\ __user\ *\ " "uaddr" ", unsigned\ int\ " "flags" ", u32\ " "val" ", ktime_t\ *\ " "abs_time" ", u32\ " "bitset" ", u32\ __user\ *\ " "uaddr2" ");"
.SH "ARGUMENTS"
.PP
\fIu32 __user * uaddr\fR
.RS 4
the futex we initially wait on (non\-pi)
.RE
.PP
\fIunsigned int flags\fR
.RS 4
futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc\&.), they must be the same type, no requeueing from private to shared, etc\&.
.RE
.PP
\fIu32 val\fR
.RS 4
the expected value of uaddr
.RE
.PP
\fIktime_t * abs_time\fR
.RS 4
absolute timeout
.RE
.PP
\fIu32 bitset\fR
.RS 4
32 bit wakeup bitset set by userspace, defaults to all
.RE
.PP
\fIu32 __user * uaddr2\fR
.RS 4
the pi futex we will take prior to returning to user\-space
.RE
.SH "DESCRIPTION"
.PP
The caller will wait on uaddr and will be requeued by
\fBfutex_requeue\fR
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\&.
.PP
We call schedule in
\fBfutex_wait_queue_me\fR
when we enqueue and return there via the following\-\- 1) wakeup on uaddr2 after an atomic lock acquisition by
\fBfutex_requeue\fR
2) wakeup on uaddr2 after a requeue 3) signal 4) timeout
.PP
If 3, cleanup and return \-ERESTARTNOINTR\&.
.PP
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
.PP
If 6, return \-EWOULDBLOCK (restarting the syscall would do the same)\&.
.PP
If 4 or 7, we cleanup and return with \-ETIMEDOUT\&.
.SH "RETURN"
.PP
0 \- On success; <0 \- On error
.SH "AUTHOR"
.PP
\fBRusty Russell\fR <\&rusty@rustcorp.com.au\&>
.RS 4
Author.
.RE
.SH "COPYRIGHT"
.br