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From: Jackie Liu <liuyun01@kylinos.cn>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Subject: Re: [PATCH 1/2] io_uring: fix issue when IOSQE_IO_DRAIN pass with IOSQE_IO_LINK
Date: Fri, 16 Aug 2019 08:48:05 +0800
Message-ID: <6EC9DDF3-3142-4FE1-831B-E5A823FBFC51@kylinos.cn> (raw)
In-Reply-To: <d72a6911-d1fb-5c88-7992-8d4715ddbcc8@kernel.dk>


ÔÚ 2019Äê8ÔÂ16ÈÕ£¬01:07£¬Jens Axboe <axboe@kernel.dk> дµÀ£º

> 
> On 8/14/19 3:35 AM, Jackie Liu wrote:
>> Suppose there are three IOs here, and their order is as follows:
>> 
>> Submit:
>> 	[1] IO_LINK
>> 	    |
>> 	    |---  [2] IO_LINK | IO_DRAIN
>> 		      |
>> 		      |- [3] NORMAL_IO
>> 
>> In theory, they all need to be inserted into the Link-list, but flag
>> IO_DRAIN we have, io[2] and io[3] will be inserted into the defer_list,
>> and finally, io[3] and io[2] will be processed at the same time.
>> 
>> Now, it is directly forbidden to pass these two flags at the same time.
>> 
>> Fixes: 9e645e1105c ("io_uring: add support for sqe links")
>> Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
>> ---
>>  fs/io_uring.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index d542f1c..05ee628 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -2074,10 +2074,13 @@ static void io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
>>  {
>>  	struct io_uring_sqe *sqe_copy;
>>  	struct io_kiocb *req;
>> +	unsigned int flags;
>>  	int ret;
>> 
>> +	flags = READ_ONCE(s->sqe->flags);
>>  	/* enforce forwards compatibility on users */
>> -	if (unlikely(s->sqe->flags & ~SQE_VALID_FLAGS)) {
>> +	if (unlikely((flags & ~SQE_VALID_FLAGS) ||
>> +		     (flags & (IOSQE_IO_DRAIN | IOSQE_IO_LINK)))) {
> 
> This doesn't look right, as any setting of either DRAIN or LINK would now
> fail?
> 
> Did you mean something ala:
> 
> 	if ((flags & (IOSQE_IO_DRAIN | IOSQE_IO_LINK)) ==
> 	    (IOSQE_IO_DRAIN | IOSQE_IO_LINK)) {
> 		... fail ...
> 	}
> 
> which makes me worried that you didn't test this at all...
> 
> -- 
> Jens Axboe

Oh, yes, it's my fault, I just simulated it in my head, thank you for pointing out.
I think I'd add an [RFC PATCH] next time. 

For this issue, I have two solutions, first is this, just avoid passing DRAIN and LINK at
the same time; second is allow, let the SQE following LINK inherit the DRAIN flag, but
It's more complicated, I prefer the first one.

I will rewrite this patch later, with a real test. Thanks again.

--
Jackie Liu




  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14  9:35 Jackie Liu
2019-08-14  9:35 ` [PATCH 2/2] io_uring: fix an issue when IOSQE_IO_LINK is inserted into defer list Jackie Liu
2019-08-15 17:21   ` Jens Axboe
2019-08-15 17:07 ` [PATCH 1/2] io_uring: fix issue when IOSQE_IO_DRAIN pass with IOSQE_IO_LINK Jens Axboe
2019-08-16  0:48   ` Jackie Liu [this message]
2019-08-16  1:21     ` Jens Axboe
2019-08-16  6:47       ` Jackie Liu

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