linux.git/kernel/futex/futex.h, branch v6.9

futex: make the vectored futex operations available

2023-09-29T08:37:07+00:00

Rename unqueue_multiple() as futex_unqueue_multiple(), and make both
that and futex_wait_multiple_setup() available for external users. This
is in preparation for wiring up vectored waits in io_uring.

Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: make futex_parse_waitv() available as a helper

2023-09-29T08:37:05+00:00

To make it more generically useful, augment it with allowing the caller
to pass in the wake handler and wake data. Convert the futex_waitv()
syscall, passing in the default handlers.

Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: add wake_data to struct futex_q

2023-09-29T08:37:01+00:00

With handling multiple futex_q for waitv, we cannot easily go from the
futex_q to data related to that request or queue. Add a wake_data
argument that belongs to the wake handler assigned.

Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: abstract out a __futex_wake_mark() helper

2023-09-29T08:36:54+00:00

Move the unqueue and lock_ptr clear into a helper that futex_wake_mark()
calls. Add it to the public functions as well, in preparation for using
it outside the core futex code.

Suggested-by: Peter Zijlstra 
Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: factor out the futex wake handling

2023-09-29T08:36:50+00:00

In preparation for having another waker that isn't futex_wake_mark(),
add a wake handler in futex_q. No extra data is associated with the
handler outside of struct futex_q itself. futex_wake_mark() is defined as
the standard wakeup helper, now set through futex_q_init like other
defaults.

Normal sync futex waiting relies on wake_q holding tasks that should
be woken up. This is what futex_wake_mark() does, it'll unqueue the
futex and add the associated task to the wake queue. For async usage of
futex waiting, rather than having tasks sleeping on the futex, we'll
need to deal with a futex wake differently. For the planned io_uring
case, that means posting a completion event for the task in question.
Having a definable wake handler can help support that use case.

Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: move FUTEX2_VALID_MASK to futex.h

2023-09-29T08:36:16+00:00

We need this for validating the futex2 flags outside of the normal
futex syscalls.

Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe

futex: Add flags2 argument to futex_requeue()

2023-09-21T17:22:09+00:00

In order to support mixed size requeue, add a second flags argument to
the internal futex_requeue() function.

No functional change intended.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20230921105248.396780136@noisy.programming.kicks-ass.net

futex: Propagate flags into get_futex_key()

2023-09-21T17:22:09+00:00

Instead of only passing FLAGS_SHARED as a boolean, pass down flags as
a whole.

No functional change intended.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20230921105248.282857501@noisy.programming.kicks-ass.net

futex: Add sys_futex_wait()

2023-09-21T17:22:08+00:00

To complement sys_futex_waitv()/wake(), add sys_futex_wait(). This
syscall implements what was previously known as FUTEX_WAIT_BITSET
except it uses 'unsigned long' for the value and bitmask arguments,
takes timespec and clockid_t arguments for the absolute timeout and
uses FUTEX2 flags.

The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Acked-by: Geert Uytterhoeven 
Link: https://lore.kernel.org/r/20230921105248.164324363@noisy.programming.kicks-ass.net

futex: FLAGS_STRICT

2023-09-21T17:22:07+00:00

The current semantics for futex_wake() are a bit loose, specifically
asking for 0 futexes to be woken actually gets you 1.

Adding a !nr check to sys_futex_wake() makes that it would return 0
for unaligned futex words, because that check comes in the shared
futex_wake() function. Adding the !nr check there, would affect the
legacy sys_futex() semantics.

Hence frob a flag :-(

Suggested-by: André Almeida 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20230921105248.048643656@noisy.programming.kicks-ass.net