Re: [PATCH 3/3] io_uring: allow POLL_ADD with double poll_wait() users

[Jens Axboe <axboe@kernel.dk>]

On 2/11/20 1:22 PM, Pavel Begunkov wrote:
>> @@ -3692,15 +3738,33 @@ static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
>>  			       struct poll_table_struct *p)
>>  {
>>  	struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
>> +	struct io_kiocb *req = pt->req;
>> +	struct io_poll_iocb *poll = &req->poll;
>>  
>> -	if (unlikely(pt->req->poll.head)) {
>> -		pt->error = -EINVAL;
>> -		return;
>> +	/*
>> +	 * If poll->head is already set, it's because the file being polled
>> +	 * use multiple waitqueues for poll handling (eg one for read, one
>> +	 * for write). Setup a separate io_poll_iocb if this happens.
>> +	 */
>> +	if (unlikely(poll->head)) {
> 
> I'll keep looking, but I guess there should be :
> 
> if (req->io)
> 	return -EINVAL;

Yes, I've changed it to:

if (unlikely(poll->head)) {
	/* already have a 2nd entry, fail a third attempt */
	if (req->io) {
		pt->error = -EINVAL;
		return;
	}
	poll = kmalloc(sizeof(*poll), GFP_ATOMIC);
	if (!poll) {
		pt->error = -ENOMEM;
		return;
	}
	[...]

-- 
Jens Axboe