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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe