From: Andy Lutomirski <luto@amacapital.net>
To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
raven@themaw.net, Christian Brauner <christian@brauner.io>,
keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
linux-block <linux-block@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 11/10] pipe: Add fsync() support [ver #2]
Date: Sat, 2 Nov 2019 13:31:10 -0700 [thread overview]
Message-ID: <CC3328CC-2F05-461E-AAC3-8DEBAB1BA162@amacapital.net> (raw)
In-Reply-To: <25886.1572723272@warthog.procyon.org.uk>
> On Nov 2, 2019, at 12:34 PM, David Howells <dhowells@redhat.com> wrote:
>
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>>>> Similar synchronization is required for reusing memory after vmsplice()?
>>>> I don't see other way how sender could safely change these pages.
>
> Actually, it's probably worse than that. If the output of the pipe gets teed
> or spliced somewhere else, you still don't know when the vmspliced pages are
> finished with.
>
>
I sometimes wonder whether vmsplice should be disallowed or severely restricted. Even ignoring these usability issues, it makes me very uncomfortable that you can have some data queue up on a pipe, tee() it, and get *different* data in the original pipe and the teed copy because the sender used vmsplice and is messing with you.
Add in the fact that it’s not obvious that vmsplice *can* be used correctly, and I’m wondering if we should just remove it or make it just do write() under the hood.
I suppose the kernel could guarantee that it stops referring to the vmsplice source pages as soon as anything sees *or* tees the data. This way it would be, at least in principle, possible to say “hey, the pipe has consumed the first n vmspliced bytes, so I can reuse that memory”.
WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@amacapital.net>
To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
raven@themaw.net, Christian Brauner <christian@brauner.io>,
keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
linux-block <linux-block@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 11/10] pipe: Add fsync() support [ver #2]
Date: Sat, 02 Nov 2019 20:31:10 +0000 [thread overview]
Message-ID: <CC3328CC-2F05-461E-AAC3-8DEBAB1BA162@amacapital.net> (raw)
In-Reply-To: <25886.1572723272@warthog.procyon.org.uk>
> On Nov 2, 2019, at 12:34 PM, David Howells <dhowells@redhat.com> wrote:
>
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>>>> Similar synchronization is required for reusing memory after vmsplice()?
>>>> I don't see other way how sender could safely change these pages.
>
> Actually, it's probably worse than that. If the output of the pipe gets teed
> or spliced somewhere else, you still don't know when the vmspliced pages are
> finished with.
>
>
I sometimes wonder whether vmsplice should be disallowed or severely restricted. Even ignoring these usability issues, it makes me very uncomfortable that you can have some data queue up on a pipe, tee() it, and get *different* data in the original pipe and the teed copy because the sender used vmsplice and is messing with you.
Add in the fact that it’s not obvious that vmsplice *can* be used correctly, and I’m wondering if we should just remove it or make it just do write() under the hood.
I suppose the kernel could guarantee that it stops referring to the vmsplice source pages as soon as anything sees *or* tees the data. This way it would be, at least in principle, possible to say “hey, the pipe has consumed the first n vmspliced bytes, so I can reuse that memory”.
next prev parent reply other threads:[~2019-11-02 20:31 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-23 20:17 [RFC PATCH 00/10] pipe: Notification queue preparation [ver #2] David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 01/10] pipe: Reduce #inclusion of pipe_fs_i.h " David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 02/10] Remove the nr_exclusive argument from __wake_up_sync_key() " David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 03/10] Add wake_up_interruptible_sync_poll_locked() " David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-26 0:29 ` kbuild test robot
2019-10-26 0:50 ` kbuild test robot
2019-10-26 14:58 ` [pipe] 6567a02d20: BUG:kernel_NULL_pointer_dereference,address kernel test robot
2019-10-26 14:58 ` kernel test robot
2019-10-26 14:58 ` kernel test robot
2019-10-27 14:03 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2] Linus Torvalds
2019-10-27 14:03 ` Linus Torvalds
2019-10-30 16:19 ` Ilya Dryomov
2019-10-30 16:19 ` Ilya Dryomov
2019-10-30 20:35 ` Rasmus Villemoes
2019-10-30 20:35 ` Rasmus Villemoes
2019-10-30 22:16 ` Ilya Dryomov
2019-10-30 22:16 ` Ilya Dryomov
2019-10-30 22:38 ` Rasmus Villemoes
2019-10-30 22:38 ` Rasmus Villemoes
2019-10-31 15:11 ` David Howells
2019-10-31 15:57 ` Ilya Dryomov
2019-10-31 15:57 ` Ilya Dryomov
2019-11-01 14:53 ` David Howells
2019-10-31 14:57 ` David Howells
2019-11-03 11:17 ` Matthew Wilcox
2019-11-03 11:17 ` Matthew Wilcox
2019-12-06 21:47 ` Johannes Hirte
2019-12-06 21:47 ` Johannes Hirte
2019-12-06 22:14 ` Linus Torvalds
2019-12-06 22:14 ` Linus Torvalds
2019-12-07 0:00 ` Johannes Hirte
2019-12-07 0:00 ` Johannes Hirte
2019-12-07 1:03 ` Linus Torvalds
2019-12-07 1:03 ` Linus Torvalds
2019-12-08 17:56 ` Johannes Hirte
2019-12-08 17:56 ` Johannes Hirte
2019-12-08 18:10 ` Linus Torvalds
2019-12-08 18:10 ` Linus Torvalds
2019-12-07 6:47 ` Linus Torvalds
2019-12-07 6:47 ` Linus Torvalds
2019-12-06 22:15 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 05/10] pipe: Allow pipes to have kernel-reserved slots " David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:17 ` David Howells
2019-10-23 20:18 ` [RFC PATCH 06/10] pipe: Advance tail pointer inside of wait spinlock in pipe_read() " David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` [RFC PATCH 07/10] pipe: Conditionalise wakeup " David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` David Howells
2019-10-27 15:57 ` Konstantin Khlebnikov
2019-10-27 15:57 ` Konstantin Khlebnikov
2019-10-31 15:21 ` David Howells
2019-10-31 16:38 ` David Howells
2019-11-03 11:04 ` Konstantin Khlebnikov
2019-11-03 11:04 ` Konstantin Khlebnikov
2019-10-23 20:18 ` [RFC PATCH 08/10] pipe: Rearrange sequence in pipe_write() to preallocate slot " David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` [RFC PATCH 09/10] pipe: Remove redundant wakeup from pipe_write() " David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock in " David Howells
2019-10-23 20:18 ` David Howells
2019-10-23 20:18 ` David Howells
2019-10-24 10:32 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-24 10:32 ` David Howells
2019-10-24 13:14 ` [RFC PATCH 00/10] pipe: Notification queue preparation " Peter Zijlstra
2019-10-24 13:14 ` Peter Zijlstra
2019-10-24 16:57 ` [RFC PATCH 11/10] pipe: Add fsync() support " David Howells
2019-10-24 16:57 ` David Howells
2019-10-24 21:29 ` Linus Torvalds
2019-10-24 21:29 ` Linus Torvalds
2019-10-25 8:34 ` David Howells
2019-10-25 8:34 ` David Howells
2019-10-27 15:22 ` Christoph Hellwig
2019-10-27 15:22 ` Christoph Hellwig
2019-10-27 16:04 ` Konstantin Khlebnikov
2019-10-27 16:04 ` Konstantin Khlebnikov
2019-10-31 15:13 ` David Howells
2019-10-31 15:15 ` David Howells
2019-11-02 18:53 ` Linus Torvalds
2019-11-02 18:53 ` Linus Torvalds
2019-11-02 19:34 ` David Howells
2019-11-02 20:31 ` Andy Lutomirski [this message]
2019-11-02 20:31 ` Andy Lutomirski
2019-11-02 22:03 ` Linus Torvalds
2019-11-02 22:03 ` Linus Torvalds
2019-11-02 22:09 ` Linus Torvalds
2019-11-02 22:09 ` Linus Torvalds
2019-11-02 22:30 ` Andy Lutomirski
2019-11-02 22:30 ` Andy Lutomirski
2019-11-02 23:02 ` Linus Torvalds
2019-11-02 23:02 ` Linus Torvalds
2019-11-02 23:09 ` Linus Torvalds
2019-11-02 23:09 ` Linus Torvalds
2019-11-02 23:14 ` Andy Lutomirski
2019-11-02 23:14 ` Andy Lutomirski
2019-11-03 12:02 ` Konstantin Khlebnikov
2019-11-03 12:02 ` Konstantin Khlebnikov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CC3328CC-2F05-461E-AAC3-8DEBAB1BA162@amacapital.net \
--to=luto@amacapital.net \
--cc=christian@brauner.io \
--cc=dhowells@redhat.com \
--cc=gregkh@linuxfoundation.org \
--cc=keyrings@vger.kernel.org \
--cc=khlebnikov@yandex-team.ru \
--cc=linux-api@vger.kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=linux@rasmusvillemoes.dk \
--cc=nicolas.dichtel@6wind.com \
--cc=peterz@infradead.org \
--cc=raven@themaw.net \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.