Re: [PATCH 1/3] io_uring: simplify io_mem_alloc return values

[Jens Axboe <axboe@kernel.dk>]

On 3/13/24 5:43 PM, Gabriel Krisman Bertazi wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>> On 3/13/24 4:32 PM, Gabriel Krisman Bertazi wrote:
>>> Pavel Begunkov <asml.silence@gmail.com> writes:
>>>
>>>> io_mem_alloc() returns a pointer on success and a pointer-encoded error
>>>> otherwise. However, it can only fail with -ENOMEM, just return NULL on
>>>> failure. PTR_ERR is usually pretty error prone.
>>>>
>>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>>> ---
>>>>  io_uring/io_uring.c | 14 +++++---------
>>>>  io_uring/kbuf.c     |  4 ++--
>>>>  2 files changed, 7 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>>> index e7d7a456b489..1d0eac0cc8aa 100644
>>>> --- a/io_uring/io_uring.c
>>>> +++ b/io_uring/io_uring.c
>>>> @@ -2802,12 +2802,8 @@ static void io_rings_free(struct io_ring_ctx *ctx)
>>>>  void *io_mem_alloc(size_t size)
>>>>  {
>>>>  	gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;
>>>> -	void *ret;
>>>>  
>>>> -	ret = (void *) __get_free_pages(gfp, get_order(size));
>>>> -	if (ret)
>>>> -		return ret;
>>>> -	return ERR_PTR(-ENOMEM);
>>>> +	return (void *) __get_free_pages(gfp, get_order(size));
>>>>  }
>>>>  
>>>>  static unsigned long rings_size(struct io_ring_ctx *ctx, unsigned int sq_entries,
>>>> @@ -3762,8 +3758,8 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
>>>>  	else
>>>>  		rings = io_rings_map(ctx, p->cq_off.user_addr, size);
>>>>  
>>>> -	if (IS_ERR(rings))
>>>> -		return PTR_ERR(rings);
>>>> +	if (!rings)
>>>> +		return -ENOMEM;
>>>>
>>>
>>> Sorry, I started reviewing this, got excited about the error path quick
>>> fix, and didn't finish the review before it got it.
>>>
>>> I think this change is broken for the ctx->flags & IORING_SETUP_NO_MMAP
>>> case, because io_rings_map returns ERR_PTR, and not NULL.  In addition,
>>> io_rings_map might fail for multiple reasons, and we want to propagate
>>> the different error codes up here.
>>
>> Yeah, see my reply from some hours ago. I dropped it back then.
> 
> ah, thanks.  I've configured lei to fetch the io_uring list every few
> hours. This ended up fetching part of the thread at first, and I only saw
> it dropped in the next fetch, after I sent the email. sorry for the noise.

Oh it's fine, I'd rather have one extra review than none at all :-)

-- 
Jens Axboe