linux-kernel - Re: [PATCH 06/10] io_uring: add support for futex wake and wait

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Message-ID: <28a42d23-6d70-bc4c-5abc-0b3cc5d7338d@kernel.dk>
Date:   Tue, 25 Jul 2023 07:48:30 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        andres@...razel.de
Subject: Re: [PATCH 06/10] io_uring: add support for futex wake and wait

On 7/25/23 7:00?AM, Peter Zijlstra wrote:
> On Fri, Jul 21, 2023 at 09:29:14AM -0600, Jens Axboe wrote:
> 
>> FWIW, here's the io_uring incremental after that rebase. Update the
>> liburing futex branch as well, updating the prep helpers to take 64 bit
>> values for mask/val and also add the flags argument that was missing as
>> well. Only other addition was adding those 4 new patches instead of the
>> old 3 ones, and adding single patch that just moves FUTEX2_MASK to
>> futex.h.
>>
>> All checks out fine, tests pass and it works.
>>
>>
>> diff --git a/io_uring/futex.c b/io_uring/futex.c
>> index 93df54dffaa0..4c9f2c841b98 100644
>> --- a/io_uring/futex.c
>> +++ b/io_uring/futex.c
>> @@ -18,11 +18,11 @@ struct io_futex {
>>  		u32 __user			*uaddr;
>>  		struct futex_waitv __user	*uwaitv;
>>  	};
>> +	unsigned long	futex_val;
>> +	unsigned long	futex_mask;
>>  	unsigned long	futexv_owned;
>> +	u32		futex_flags;
>> +	unsigned int	futex_nr;
>>  };
>>  
>>  struct io_futex_data {
>> @@ -171,15 +171,28 @@ bool io_futex_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
>>  int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>  {
>>  	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
>> +	u32 flags;
>>  
>> +	if (unlikely(sqe->fd || sqe->buf_index || sqe->file_index))
>>  		return -EINVAL;
>>  
>>  	iof->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
>> +	iof->futex_val = READ_ONCE(sqe->addr2);
>> +	iof->futex_mask = READ_ONCE(sqe->addr3);
>> +	iof->futex_nr = READ_ONCE(sqe->len);
>> +	if (iof->futex_nr && req->opcode != IORING_OP_FUTEX_WAITV)
>> +		return -EINVAL;
>> +
> 
> Hmm, would something like:
> 
> 	if (req->opcode == IORING_OP_FUTEX_WAITV) {
> 		if (iof->futex_val && iof->futex_mask)
> 			return -EINVAL;
> 
> 		/* sys_futex_waitv() doesn't take @flags as of yet */
> 		if (iof->futex_flags)
> 			return -EINVAL;
> 
> 		if (!iof->futex_nr)
> 			return -EINVAL;
> 
> 	} else {
> 		/* sys_futex_{wake,wait}() don't take @nr */
> 		if (iof->futex_nr)
> 			return -EINVAL;
> 
> 		/* both take @flags and @mask */
> 		flags = READ_ONCE(sqe->futex_flags);
> 		if (flags & ~FUTEX2_MASK)
> 			return -EINVAL;
> 
> 		iof->futex_flags = futex2_to_flags(flags);
> 		if (!futex_flags_valid(iof->futex_flags))
> 			return -EINVAL;
> 
> 		if (!futex_validate_input(iof->futex_flags, iof->futex_mask))
> 			return -EINVAL;
> 
> 		/* sys_futex_wait() takes @val */
> 		if (req->iocode == IORING_OP_FUTEX_WAIT) {
> 			if (!futex_validate_input(iof->futex_flags, iof->futex_val))
> 				return -EINVAL;
> 		} else {
> 			if (iof->futex_val)
> 				return -EINVAL;
> 		}
> 	}
> 
> work? The waitv thing is significantly different from the other two.

I think I'll just have prep and prepv totally separate. It only makes
sense to share parts of them if one is a subset of the other. That'll
get rid of the odd conditionals and sectioning of it.

-- 
Jens Axboe