linux-kernel - Re: Linux 5.19-rc7 liburing test `poll-mshot-overflow.t` and `read-write.t` fail

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Message-ID: <fbf3911151dd3cbf875b8d2a4b9e7ad4b31c80d2.camel@fb.com>
Date:   Thu, 21 Jul 2022 13:14:32 +0000
From:   Dylan Yudaken <dylany@...com>
To:     "ammarfaizi2@...weeb.org" <ammarfaizi2@...weeb.org>
CC:     "gwml@...r.gnuweeb.org" <gwml@...r.gnuweeb.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "fernandafmr12@...weeb.org" <fernandafmr12@...weeb.org>,
        "asml.silence@...il.com" <asml.silence@...il.com>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Linux 5.19-rc7 liburing test `poll-mshot-overflow.t` and
 `read-write.t` fail

On Thu, 2022-07-21 at 20:08 +0700, Ammar Faizi wrote:
> On 7/21/22 7:05 PM, Dylan Yudaken wrote:
> > It seems to be a problem with blocking reads, buffer select and
> > READV.
> > My guess is that ext4/xfs are not blocking.
> > 
> > in b66e65f41426 ("io_uring: never call io_buffer_select() for a
> > buffer
> > re-select"), this line was added in __io_iov_buffer_select
> > 
> > -       iov[0].iov_len = len;
> > +       req->rw.len = iov[0].iov_len = len;
> > 
> > Basically stashing the buffer length in rw.len. The problem is that
> > the
> > next time around that breaks at
> > 
> >          if (req->rw.len != 1)
> >                  return -EINVAL;
> > 
> > 
> > The below fixes it as an example, but it's not great. Maybe someone
> > can
> > figure out a better patch? Otherwise I can try tomorrow:
> 
> It's 8:05 PM from my end. I'll try to play with your patch after
> dinner
> while waiting for others say something.
> 

I've just sent the below actually which is a bit simpler. I reran all
the tests on btrfs and xfs and it seems to work now:

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a01ea49f3017..b0180679584f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1737,6 +1737,14 @@ static void io_kbuf_recycle(struct io_kiocb
*req, unsigned issue_flags)
            (req->flags & REQ_F_PARTIAL_IO))
                return;
 
+       /*
+        * READV uses fields in `struct io_rw` (len/addr) to stash the
selected
+        * buffer data. However if that buffer is recycled the original
request
+        * data stored in addr is lost. Therefore forbid recycling for
now.
+        */
+       if (req->opcode == IORING_OP_READV)
+               return;
+
        /*
         * We don't need to recycle for REQ_F_BUFFER_RING, we can just
clear
         * the flag and hence ensure that bl->head doesn't get
incremented.