Re: [PATCH 04/12] splice: lift pipe_lock out of splice_to_pipe()

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Sun, Dec 18, 2016 at 12:30 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> OK, I see what's going on - it's wait_for_space() lifted past the checks
> for lack of readers.  The fix, AFAICS, is simply

Ugh. Does it have to be duplicated?

How about just making the wait_for_space() loop be a for-loop, and writing it as

   for (;;) {
        if (unlikely(!pipe->readers)) {
                send_sig(SIGPIPE, current, 0);
                return -EPIPE;
        }
        if (pipe->nrbufs == pipe->buffers)
                return 0;
        if (flags & SPLICE_F_NONBLOCK)
                return -EAGAIN;
        if (signal_pending(current))
                return -ERESTARTSYS;
        pipe->waiting_writers++;
        pipe_wait(pipe);
        pipe->waiting_writers--;
   }

and just having it once?

Regardless - Andreas, can you verify that that fixes your issues? I'm
assuming you had some real load that made you notice this, not just he
dummy example..

            Linus