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From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>, [email protected]
Subject: Re: [PATCH 7/8] io_uring: fix sequencing issues with linked timeouts
Date: Tue, 19 Nov 2019 15:13:07 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 11/19/19 1:51 PM, Pavel Begunkov wrote:
> On 16/11/2019 04:53, Jens Axboe wrote:
>> We have an issue with timeout links that are deeper in the submit chain,
>> because we only handle it upfront, not from later submissions. Move the
>> prep + issue of the timeout link to the async work prep handler, and do
>> it normally for non-async queue. If we validate and prepare the timeout
>> links upfront when we first see them, there's nothing stopping us from
>> supporting any sort of nesting.
>>
>> Fixes: 2665abfd757f ("io_uring: add support for linked SQE timeouts")
>> Reported-by: Pavel Begunkov <[email protected]>
>> Signed-off-by: Jens Axboe <[email protected]>
>> ---
> 
>> @@ -923,6 +942,7 @@ static void io_fail_links(struct io_kiocb *req)
>>   			io_cqring_fill_event(link, -ECANCELED);
>>   			__io_double_put_req(link);
>>   		}
>> +		kfree(sqe_to_free);
>>   	}
>>   
>>   	io_commit_cqring(ctx);
>> @@ -2668,8 +2688,12 @@ static void io_wq_submit_work(struct io_wq_work **workptr)
>>   
>>   	/* if a dependent link is ready, pass it back */
>>   	if (!ret && nxt) {
>> -		io_prep_async_work(nxt);
>> +		struct io_kiocb *link;
>> +
>> +		io_prep_async_work(nxt, &link);
>>   		*workptr = &nxt->work;
> Are we safe here without synchronisation?
> Probably io_link_timeout_fn() may miss the new value
> (doing io-wq cancel).

Miss what new value? Don't follow that part.

This should be safe, by the time the request is findable, we have
made the necessary setup in io_prep_async_work().

-- 
Jens Axboe


  reply	other threads:[~2019-11-19 22:13 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-16  1:53 [PATCHSET] Pending io_uring items not yet queued up for 5.5 Jens Axboe
2019-11-16  1:53 ` [PATCH 1/8] io-wq: remove now redundant struct io_wq_nulls_list Jens Axboe
2019-11-16  1:53 ` [PATCH 2/8] io_uring: make POLL_ADD/POLL_REMOVE scale better Jens Axboe
2019-11-16  1:53 ` [PATCH 3/8] io_uring: io_async_cancel() should pass in 'nxt' request pointer Jens Axboe
2019-11-16  1:53 ` [PATCH 4/8] io_uring: cleanup return values from the queueing functions Jens Axboe
2019-11-16  1:53 ` [PATCH 5/8] io_uring: make io_double_put_req() use normal completion path Jens Axboe
2019-11-16  1:53 ` [PATCH 6/8] io_uring: make req->timeout be dynamically allocated Jens Axboe
2019-11-16  1:53 ` [PATCH 7/8] io_uring: fix sequencing issues with linked timeouts Jens Axboe
2019-11-19 20:51   ` Pavel Begunkov
2019-11-19 22:13     ` Jens Axboe [this message]
2019-11-20 12:42       ` Pavel Begunkov
2019-11-20 17:19         ` Jens Axboe
2019-11-20 18:15           ` Jens Axboe
2019-11-16  1:53 ` [PATCH 8/8] io_uring: remove dead REQ_F_SEQ_PREV flag Jens Axboe

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