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From:   Andrei Vagin <avagin@gmail.com>
Date:   Mon, 2 May 2022 00:01:46 -0700
Message-ID: <CANaxB-wcf0Py9eCeA8YKcBSnwzW6pKAD5edCDUadebmo=JLYhA@mail.gmail.com>
Subject: Re: [PATCH] fs: sendfile handles O_NONBLOCK of out_fd
To:     LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-fsdevel <linux-fsdevel@vger.kernel.org>, stable@kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Andrew, could you take a look at this patch?

Here is a small reproducer for the problem:

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/sendfile.h>


#define FILE_SIZE (1UL << 30)
int main(int argc, char **argv) {
        int p[2], fd;

        if (pipe2(p, O_NONBLOCK))
                return 1;

        fd = open(argv[1], O_RDWR | O_TMPFILE, 0666);
        if (fd < 0)
                return 1;
        ftruncate(fd, FILE_SIZE);

        if (sendfile(p[1], fd, 0, FILE_SIZE) == -1) {
                fprintf(stderr, "FAIL\n");
        }
        if (sendfile(p[1], fd, 0, FILE_SIZE) != -1 || errno != EAGAIN) {
                fprintf(stderr, "FAIL\n");
        }
        return 0;
}

It worked before b964bf53e540, it is stuck after b964bf53e540, and it
works again with this fix.

Thanks,
Andrei

On Thu, Apr 14, 2022 at 5:50 PM Andrei Vagin <avagin@gmail.com> wrote:
>
> sendfile has to return EAGAIN if out_fd is nonblocking and the write
> into it would block.
>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: stable@kernel.org
> Fixes: b964bf53e540 ("teach sendfile(2) to handle send-to-pipe directly")
> Signed-off-by: Andrei Vagin <avagin@gmail.com>
> ---
>  fs/read_write.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index e643aec2b0ef..ee59419cbf0f 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1247,6 +1247,9 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
>                                           count, fl);
>                 file_end_write(out.file);
>         } else {
> +               if (out.file->f_flags & O_NONBLOCK)
> +                       fl |= SPLICE_F_NONBLOCK;
> +
>                 retval = splice_file_to_pipe(in.file, opipe, &pos, count, fl);
>         }
>
> --
> 2.35.1
>