Re: [PATCH 1/7] futex: abstract out futex_op_to_flags() helper

Peter Zijlstra
2023-07-12T08:19:45Z

On Tue, Jul 11, 2023 at 06:46:59PM -0600, Jens Axboe wrote:
> Rather than needing to duplicate this for the io_uring hook of futexes,
> abstract out a helper.
>
> No functional changes intended in this patch.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> kernel/futex/futex.h | 15 +++++++++++++++
> kernel/futex/syscalls.c | 11 ++---------
> 2 files changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
> index b5379c0e6d6d..d2949fca37d1 100644
> --- a/kernel/futex/futex.h
> +++ b/kernel/futex/futex.h
> @@ -291,4 +291,19 @@ extern int futex_unlock_pi(u32 __user *uaddr, unsigned int flags);
>
> extern int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock);
>
> +static inline bool futex_op_to_flags(int op, int cmd, unsigned int *flags)
> +{
*flags = 0;

> + if (!(op & FUTEX_PRIVATE_FLAG))
> + *flags |= FLAGS_SHARED;
> +
> + if (op & FUTEX_CLOCK_REALTIME) {
> + *flags |= FLAGS_CLOCKRT;
> + if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
> + cmd != FUTEX_LOCK_PI2)
> + return false;
> + }
> +
> + return true;
> +}

> diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
> index a8074079b09e..75ca8c41cc94 100644
> --- a/kernel/futex/syscalls.c
> +++ b/kernel/futex/syscalls.c
> @@ -88,15 +88,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
> int cmd = op & FUTEX_CMD_MASK;
> unsigned int flags = 0;

and skip the initializer here.

>
> - if (!(op & FUTEX_PRIVATE_FLAG))
> - flags |= FLAGS_SHARED;
> -
> - if (op & FUTEX_CLOCK_REALTIME) {
> - flags |= FLAGS_CLOCKRT;
> - if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
> - cmd != FUTEX_LOCK_PI2)
> - return -ENOSYS;
> - }
> + if (!futex_op_to_flags(op, cmd, &flags))
> + return -ENOSYS;
>

then the helper is more self sufficient and doesn't rely on the caller
to initialize the flags word.