On Fri, May 13, 2022 at 12:23 PM Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>
> The quilt patch titled
> Subject: fs: sendfile handles O_NONBLOCK of out_fd
> has been removed from the -mm tree. Its filename was
> fs-sendfile-handles-o_nonblock-of-out_fd.patch
>
> This patch was dropped because it was merged into the mm-nonmm-stable branch\nof git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Andrew, sorry for bothering you. I can't find this patch in mm-nonmm-stable
and it has not been merged to the Linus' tree. Do I miss something?
>
> ------------------------------------------------------
> 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.
>
> This regression occurred because do_splice_direct() calls pipe_write
> that handles O_NONBLOCK. Here is a trace log from the reproducer:
>
> 1) | __x64_sys_sendfile64() {
> 1) | do_sendfile() {
> 1) | __fdget()
> 1) | rw_verify_area()
> 1) | __fdget()
> 1) | rw_verify_area()
> 1) | do_splice_direct() {
> 1) | rw_verify_area()
> 1) | splice_direct_to_actor() {
> 1) | do_splice_to() {
> 1) | rw_verify_area()
> 1) | generic_file_splice_read()
> 1) + 74.153 us | }
> 1) | direct_splice_actor() {
> 1) | iter_file_splice_write() {
> 1) | __kmalloc()
> 1) 0.148 us | pipe_lock();
> 1) 0.153 us | splice_from_pipe_next.part.0();
> 1) 0.162 us | page_cache_pipe_buf_confirm();
> ... 16 times
> 1) 0.159 us | page_cache_pipe_buf_confirm();
> 1) | vfs_iter_write() {
> 1) | do_iter_write() {
> 1) | rw_verify_area()
> 1) | do_iter_readv_writev() {
> 1) | pipe_write() {
> 1) | mutex_lock()
> 1) 0.153 us | mutex_unlock();
> 1) 1.368 us | }
> 1) 1.686 us | }
> 1) 5.798 us | }
> 1) 6.084 us | }
> 1) 0.174 us | kfree();
> 1) 0.152 us | pipe_unlock();
> 1) + 14.461 us | }
> 1) + 14.783 us | }
> 1) 0.164 us | page_cache_pipe_buf_release();
> ... 16 times
> 1) 0.161 us | page_cache_pipe_buf_release();
> 1) | touch_atime()
> 1) + 95.854 us | }
> 1) + 99.784 us | }
> 1) ! 107.393 us | }
> 1) ! 107.699 us | }
>
> 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
>
>
