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

Jens Axboe
2023-07-12T15:00:20Z

On 7/12/23 2:16 AM, Peter Zijlstra wrote:
> 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.

Good idea - done, thanks.

--
Jens Axboe