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: Fri, 13 Jan 2017 20:08:27 +0000 [thread overview]
Message-ID: <20170113200826.GP1555@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CA+55aFw0T1wARr8kLvcuHkA4bDE+YJ18wKtPaxc1vFHWPgfQQg@mail.gmail.com>
On Fri, Jan 13, 2017 at 11:33:18AM -0800, Linus Torvalds wrote:
> What am I missing?
The fact that we want to free the _tail_, not the beginning of the
damn thing.
> Why is "pipe_advance()" written in that incomprehensible form? Why
> don't we do the pipe_buf_release() as we advance through it, instead
> of doing it at the end?
>
> Also, the line
>
> buf->len = size;
>
> in that pipe_advance() function looks buggy. "size" is how much we
> *remove* from buf->len, shouldn't we update buf->len by subtracting
> size?
Because it's "truncate to size", not "throw everything up to that point
out".
We have some amount of data pushed into pipe (in this case - 0) and we
have some buffers allocated by ..._get_pages() past the end of it.
Some of that we want to keep (again, in this case - none) and have the next
copy_to_iter() go after those, the rest we discard.
next prev parent reply other threads:[~2017-01-13 20:08 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
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 [this message]
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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