From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Alan J. Wylie" <alan@wylie.me.uk>,
Thorsten Leemhuis <regressions@leemhuis.info>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn
Date: Thu, 12 Jan 2017 22:37:18 +0000 [thread overview]
Message-ID: <20170112223718.GA1555@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CA+55aFy+sj1SmPrTPAon-=M=DRtiS5ak0DJtQe0TMBU3sMJ0kg@mail.gmail.com>
On Thu, Jan 12, 2017 at 02:26:42PM -0800, Linus Torvalds wrote:
> On Thu, Jan 12, 2017 at 12:26 PM, Alan J. Wylie <alan@wylie.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.
FWIW, I would really like to know what kind of files had been involved.
There are two paths that can lead to default_file_splice_read():
splice_direct_to_actor() -> do_splice_to() -> default_file_splice_read() and
do_splice() -> do_splice_to() -> default_file_splice_read().
The former only gets there for regular files and block devices. The latter
is guaranteed that file is not a pipe. So
* not a socket (have ->splice_read() of their own)
* not a pipe or FIFO (neither path allows those)
* not a block device (have ->splice_read() of their own)
* not a regular file on a normal local fs (ditto)
So what is it called for in that reproducer?
next prev parent reply other threads:[~2017-01-12 22:37 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-12 20:26 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn Alan J. Wylie
2017-01-12 20:31 ` Al Viro
2017-01-12 20:38 ` Alan J. Wylie
2017-01-12 22:26 ` Linus Torvalds
2017-01-12 22:37 ` Al Viro [this message]
2017-01-12 22:46 ` Al Viro
2017-01-12 23:02 ` Linus Torvalds
2017-01-12 23:14 ` Al Viro
2017-01-12 23:14 ` Linus Torvalds
2017-01-12 23:27 ` Al Viro
2017-01-12 22:46 ` Alan J. Wylie
2017-01-12 22:58 ` Al Viro
2017-01-12 23:28 ` Linus Torvalds
2017-01-13 4:00 ` Al Viro
2017-01-13 7:38 ` Alan J. Wylie
2017-01-13 7:23 ` Alan J. Wylie
2017-01-13 9:33 ` Al Viro
2017-01-13 9:54 ` Alan J. Wylie
2017-01-13 10:20 ` Al Viro
2017-01-13 10:32 ` Alan J. Wylie
2017-01-13 11:25 ` Al Viro
2017-01-13 11:18 ` Al Viro
2017-01-13 19:33 ` Linus Torvalds
2017-01-13 20:08 ` Al Viro
2017-01-13 20:11 ` Al Viro
2017-01-13 20:32 ` Linus Torvalds
2017-01-13 20:47 ` Al Viro
2017-01-13 21:55 ` Al Viro
2017-01-13 21:59 ` Al Viro
2017-01-13 22:13 ` Al Viro
2017-01-13 22:50 ` Al Viro
2017-01-14 0:59 ` Linus Torvalds
2017-01-14 1:24 ` Al Viro
2017-01-14 1:43 ` Al Viro
2017-01-14 1:46 ` Linus Torvalds
2017-01-14 1:57 ` Al Viro
2017-01-15 0:53 ` Al Viro
2017-01-14 13:16 ` Alan J. Wylie
2017-01-14 16:29 ` Alan J. Wylie
2017-01-14 17:57 ` Linus Torvalds
2017-01-13 20:08 ` Linus Torvalds
2017-01-13 20:16 ` Al Viro
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