On 2020-09-04 22:50, Pavel Begunkov wrote:
On 05/09/2020 07:35, Jens Axboe wrote:
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, nick@xxxxxxxxxxxx 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?
Hah, absolutely the same patch was in a series I was going to send
today, but with a note that it works by luck so not a bug. Apparently,
it is :)
BTW, const in iter->iov is guarding from such cases, yet another proof
that const casts are evil.
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;
}
Thanks for the speedy replies and finding/fixing this so fast! I'm new
to kernel dev and haven't built my own yet but I think Norman is going
to try out your patch soon.
Nick
