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From: Jens Axboe <[email protected]>
To: Jonas Bonn <[email protected]>, [email protected]
Subject: Re: sendmsg fails when it 'blocks'
Date: Sun, 9 Feb 2020 09:40:33 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 2/9/20 2:25 AM, Jonas Bonn wrote:
> Hi Jens,
> 
> I've been trying to use io_uring to flood a network link with UDP 
> packets.  Essentially, the program just pushes a series of sendmsg() 
> calls through the SQE ring and keeps topping it up with new calls as 
> soon as the completions come in.
> 
> When the sendmsg() calls complete immediately then everything works 
> fine; however, when the calls 'block' and get queued up in the kernel 
> then the calls return either errno 97 or 22 when they're retried through 
> the workqueue (effectively, bad address or invalid iovec length).
> 
> My gut-feeling is that there's some issue copying the msghdr struct so 
> that the call that's retried isn't exactly the same one that was 
> requested.  I looked into the kernel code a bit, but couldn't really 
> make heads or tails of it so I though I'd ask for some input while I 
> keep investigating.
> 
> I noticed that liburing has a simple test for sendmsg that sends a 
> single message; the 'punted' case doesn't seem to be tested.  Is this 
> something you've tried?
> 
> Tested on kernels 5.3 to 5.6-pre and the behaviour's pretty much the 
> same with regards to the above.

You could try and pull:

git://git.kernel.dk/linux-block io_uring-5.6

into the current 5.6-pre tree and see if it works for you.

In any case, do you have a test case for this?


-- 
Jens Axboe


      reply	other threads:[~2020-02-09 16:40 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-09  9:25 sendmsg fails when it 'blocks' Jonas Bonn
2020-02-09 16:40 ` Jens Axboe [this message]

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