linux-kernel - Re: 4.9.0 regression in pipe-backed iov

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Message-ID: <CA+55aFy+sj1SmPrTPAon-=M=DRtiS5ak0DJtQe0TMBU3sMJ0kg@mail.gmail.com>
Date:   Thu, 12 Jan 2017 14:26:42 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Alan J. Wylie" <alan@...ie.me.uk>
Cc:     Thorsten Leemhuis <regressions@...mhuis.info>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn

On Thu, Jan 12, 2017 at 12:26 PM, Alan J. Wylie <alan@...ie.me.uk> wrote:
>
> Strace shows that the processes are hanging in write() and read() calls.

If this is splice-related, I'm assuming that they aren't actually the
two ends of the same pipe, and there is somebody doing splice in the
middle.

I'm not seeing that process. I'm assuming it's systemd.  Can you try
to find it and strace that one too? Because that middle man is likely
the one that has problems (and is not able to splice from one pipe to
the other).

Ugh. That one commit has had a lot of bugs in it already. We do not
have good splice test coverage, because almost nobody uses it.

               Linus