+ fs-sendfile-handles-o_nonblock-of-out_fd.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

The patch titled
     Subject: fs: sendfile handles O_NONBLOCK of out_fd
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     fs-sendfile-handles-o_nonblock-of-out_fd.patch

This patch should soon appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Andrei Vagin <avagin@xxxxxxxxx>
Subject: fs: sendfile handles O_NONBLOCK of out_fd

sendfile has to return EAGAIN if out_fd is nonblocking and the write into
it would block.

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.

Link: https://lkml.kernel.org/r/20220415005015.525191-1-avagin@xxxxxxxxx
Fixes: b964bf53e540 ("teach sendfile(2) to handle send-to-pipe directly")
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/read_write.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/read_write.c~fs-sendfile-handles-o_nonblock-of-out_fd
+++ a/fs/read_write.c
@@ -1247,6 +1247,9 @@ static ssize_t do_sendfile(int out_fd, i
 					  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);
 	}
 
_

Patches currently in -mm which might be from avagin@xxxxxxxxx are

fs-sendfile-handles-o_nonblock-of-out_fd.patch