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

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Date:   Thu, 21 Jul 2022 12:05:49 +0000
From:   Dylan Yudaken <dylany@...com>
To:     "ammarfaizi2@...weeb.org" <ammarfaizi2@...weeb.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "gwml@...r.gnuweeb.org" <gwml@...r.gnuweeb.org>,
        "fernandafmr12@...weeb.org" <fernandafmr12@...weeb.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "asml.silence@...il.com" <asml.silence@...il.com>,
        "io-uring@...r.kernel.org" <io-uring@...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 17:41 +0700, Ammar Faizi wrote:
> On 7/21/22 4:48 PM, Dylan Yudaken wrote:
> > What fs are you using? testing on a fresh XFS fs read-write.t works
> > for
> > me
> 
> I am using btrfs.
> 
> After I got your email, I tried to run the test on an ext4 directory
> and
> it works fine. But fails on a btrfs directory.
> 
> Any idea why does the test fail on a btrfs fs?
> 

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:

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2b7bb62c7805..d9fa226f8e30 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -647,6 +647,8 @@ struct io_rw {
        u64                             addr;
        u32                             len;
        rwf_t                           flags;
+       u64                             bufaddr;
+       u32                             buflen;
 };
 
 struct io_connect {
@@ -3899,7 +3901,7 @@ static ssize_t io_compat_import(struct io_kiocb
*req, struct iovec *iov,
                return -ENOBUFS;
        req->rw.addr = (unsigned long) buf;
        iov[0].iov_base = buf;
-       req->rw.len = iov[0].iov_len = (compat_size_t) len;
+       req->rw.buflen = iov[0].iov_len = (compat_size_t) len;
        return 0;
 }
 #endif
@@ -3920,9 +3922,9 @@ static ssize_t __io_iov_buffer_select(struct
io_kiocb *req, struct iovec *iov,
        buf = io_buffer_select(req, &len, issue_flags);
        if (!buf)
                return -ENOBUFS;
-       req->rw.addr = (unsigned long) buf;
+       req->rw.bufaddr = (unsigned long) buf;
        iov[0].iov_base = buf;
-       req->rw.len = iov[0].iov_len = len;
+       req->rw.buflen = iov[0].iov_len = len;
        return 0;
 }
 
@@ -3930,8 +3932,8 @@ static ssize_t io_iov_buffer_select(struct
io_kiocb *req, struct iovec *iov,
                                    unsigned int issue_flags)
 {
        if (req->flags & (REQ_F_BUFFER_SELECTED|REQ_F_BUFFER_RING)) {
-               iov[0].iov_base = u64_to_user_ptr(req->rw.addr);
-               iov[0].iov_len = req->rw.len;
+               iov[0].iov_base = u64_to_user_ptr(req->rw.bufaddr);
+               iov[0].iov_len = req->rw.buflen;
                return 0;
        }
        if (req->rw.len != 1)