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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 18 Dec 2016 14:10:54 -0800
Message-ID: <CA+55aFzPE6FbwX2NuiMkz9G+FzAoiNeb8jOSWwSoX3O7+KuH4Q@mail.gmail.com>
Subject: Re: [PATCH 04/12] splice: lift pipe_lock out of splice_to_pipe()
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
        Dave Chinner <david@fromorbit.com>,
        CAI Qian <caiqian@redhat.com>,
        linux-xfs <linux-xfs@vger.kernel.org>, xfs@oss.sgi.com,
        Jens Axboe <axboe@kernel.dk>, Nick Piggin <npiggin@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Sun, Dec 18, 2016 at 12:30 PM, Al Viro <viro@zeniv.linux.org.uk> 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