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

[Gabriel Krisman Bertazi <krisman@suse.de>]

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.

-- 
Gabriel Krisman Bertazi