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

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Message-ID: <20170113204731.GS1555@ZenIV.linux.org.uk>
Date:   Fri, 13 Jan 2017 20:47:31 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Alan J. Wylie" <alan@...ie.me.uk>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn

On Fri, Jan 13, 2017 at 12:32:37PM -0800, Linus Torvalds wrote:

> Ugh. I still think your patch is butt-ugly, and the index comparisons
> make me nervous, but..

No arguments here - 6am on 20-odd hours of uptime is _not_ a good time
for writing, especially since the data structure needs better documentation
and probably a couple of inlined helpers.  I'll try to massage the damn
thing into more readable form.

> Let's see if Alan's issue actually goes away with your later patch.

*nod*

I'm fairly sure this is the root cause of what's going on there, but it would
be nice to have an experimental confirmation.