在 2019年8月16日，01:07，Jens Axboe <axboe@xxxxxxxxx> 写道：
>
> 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@xxxxxxxxxx>
>> ---
>> 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
