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From: Jens Axboe <[email protected]>
To: [email protected], [email protected]
Subject: Re: WRITEV with IOSQE_ASYNC broken?
Date: Fri, 4 Sep 2020 22:35:19 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 9/4/20 9:57 PM, Jens Axboe wrote:
> On 9/4/20 9:53 PM, Jens Axboe wrote:
>> On 9/4/20 9:22 PM, [email protected] wrote:
>>> Hi,
>>>
>>> I am helping out with the netty io_uring integration, and came across 
>>> some strange behaviour which seems like it might be a bug related to 
>>> async offload of read/write iovecs.
>>>
>>> Basically a WRITEV SQE seems to fail reliably with -BADADDRESS when the 
>>> IOSQE_ASYNC flag is set but works fine otherwise (everything else the 
>>> same). This is with 5.9.0-rc3.
>>
>> Do you see it just on 5.9-rc3, or also 5.8? Just curious... But that is
>> very odd in any case, ASYNC writev is even part of the regular tests.
>> Any sort of deferral, be it explicit via ASYNC or implicit through
>> needing to retry, saves all the needed details to retry without
>> needing any of the original context.
>>
>> Can you narrow down what exactly is being written - like file type,
>> buffered/O_DIRECT, etc. What file system, what device is hosting it.
>> The more details the better, will help me narrow down what is going on.
> 
> Forgot, also size of the IO (both total, but also number of iovecs in
> that particular request.
> 
> Essentially all the details that I would need to recreate what you're
> seeing.

Turns out there was a bug in the explicit handling, new in the current
-rc series. Can you try and add the below?

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0d7be2e9d005..000ae2acfd58 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2980,14 +2980,15 @@ static inline int io_rw_prep_async(struct io_kiocb *req, int rw,
 				   bool force_nonblock)
 {
 	struct io_async_rw *iorw = &req->io->rw;
+	struct iovec *iov;
 	ssize_t ret;
 
-	iorw->iter.iov = iorw->fast_iov;
-	ret = __io_import_iovec(rw, req, (struct iovec **) &iorw->iter.iov,
-				&iorw->iter, !force_nonblock);
+	iorw->iter.iov = iov = iorw->fast_iov;
+	ret = __io_import_iovec(rw, req, &iov, &iorw->iter, !force_nonblock);
 	if (unlikely(ret < 0))
 		return ret;
 
+	iorw->iter.iov = iov;
 	io_req_map_rw(req, iorw->iter.iov, iorw->fast_iov, &iorw->iter);
 	return 0;
 }

-- 
Jens Axboe


  reply	other threads:[~2020-09-05  4:35 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-05  3:22 WRITEV with IOSQE_ASYNC broken? nick
2020-09-05  3:53 ` Jens Axboe
2020-09-05  3:57   ` Jens Axboe
2020-09-05  4:35     ` Jens Axboe [this message]
2020-09-05  5:50       ` Pavel Begunkov
2020-09-05  8:24         ` nick
2020-09-05  8:26           ` Norman Maurer
2020-09-05 14:28             ` Norman Maurer
2020-09-05 15:02               ` Jens Axboe
2020-09-05 15:10         ` Jens Axboe
2020-09-05  5:04     ` nick

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