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

[Jens Axboe]

On 7/25/23 7:48?AM, Jens Axboe wrote:
> 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.

Something like the below - totally untested, but just to show what I
mean. Will need to get split and folded into the two separate patches.
Will test and fold them later today.


diff --git a/io_uring/futex.c b/io_uring/futex.c
index 4c9f2c841b98..b0f90154d974 100644
--- a/io_uring/futex.c
+++ b/io_uring/futex.c
@@ -168,7 +168,7 @@ bool io_futex_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
 	return found;
 }
 
-int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+static 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;
@@ -179,9 +179,6 @@ int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	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;
 
 	flags = READ_ONCE(sqe->futex_flags);
 	if (flags & ~FUTEX2_MASK)
@@ -191,14 +188,36 @@ int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (!futex_flags_valid(iof->futex_flags))
 		return -EINVAL;
 
-	if (!futex_validate_input(iof->futex_flags, iof->futex_val) ||
-	    !futex_validate_input(iof->futex_flags, iof->futex_mask))
+	if (!futex_validate_input(iof->futex_flags, iof->futex_mask))
 		return -EINVAL;
 
-	iof->futexv_owned = 0;
 	return 0;
 }
 
+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);
+	int ret;
+
+	if (unlikely(sqe->len))
+		return -EINVAL;
+
+	ret = __io_futex_prep(req, sqe);
+	if (ret)
+		return ret;
+
+	/* sys_futex_wait() takes @val */
+	if (req->opcode == IORING_OP_FUTEX_WAIT) {
+		if (!futex_validate_input(iof->futex_flags, iof->futex_val))
+			return -EINVAL;
+	} else {
+		if (iof->futex_val)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 static void io_futex_wakev_fn(struct wake_q_head *wake_q, struct futex_q *q)
 {
 	struct io_kiocb *req = q->wake_data;
@@ -220,10 +239,15 @@ int io_futexv_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	struct futex_vector *futexv;
 	int ret;
 
-	ret = io_futex_prep(req, sqe);
+	ret = __io_futex_prep(req, sqe);
 	if (ret)
 		return ret;
 
+	/* No flags supported for waitv */
+	if (iof->futex_flags)
+		return -EINVAL;
+
+	iof->futex_nr = READ_ONCE(sqe->len);
 	if (!iof->futex_nr || iof->futex_nr > FUTEX_WAITV_MAX)
 		return -EINVAL;
 
@@ -238,6 +262,7 @@ int io_futexv_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return ret;
 	}
 
+	iof->futexv_owned = 0;
 	req->flags |= REQ_F_ASYNC_DATA;
 	req->async_data = futexv;
 	return 0;


-- 
Jens Axboe