linux-kernel - Re: [PATCH 1/7] futex: abstract out futex_op_to

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Message-ID: <0ae2fc52-5097-480a-d2f1-c112f1e514f3@kernel.dk>
Date:   Wed, 12 Jul 2023 08:59:47 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH 1/7] futex: abstract out futex_op_to_flags() helper

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@...nel.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