From: David Howells <dhowells@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: dhowells@redhat.com,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Casey Schaufler <casey@schaufler-ca.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
raven@themaw.net, Christian Brauner <christian@brauner.io>,
keyrings@vger.kernel.org, USB list <linux-usb@vger.kernel.org>,
linux-block <linux-block@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 04/14] pipe: Add O_NOTIFICATION_PIPE [ver #2]
Date: Fri, 08 Nov 2019 06:42:50 +0000 [thread overview]
Message-ID: <7772.1573195370@warthog.procyon.org.uk> (raw)
In-Reply-To: <CALCETrWeN9CGJHz0dzG1uH5Qjbr+xG3OKZuEd33eBY_rAzVkqQ@mail.gmail.com>
Andy Lutomirski <luto@kernel.org> wrote:
> I can open a normal pipe from userspace (with pipe() or pipe2()), and
> I can have two threads. One thread writes to the pipe with write().
> The other thread writes with splice(). Everything works fine.
Yes. Every operation you do on a pipe from userspace is serialised with the
pipe mutex - and both ends share the same pipe.
> What's special about notifications?
The post_notification() cannot take the pipe mutex. It has to be callable
from softirq context. Linus's idea is that when you're actually altering the
ring pointers you should hold the wake-queue spinlock, and post_notification()
holds the wake queue spinlock for the duration of the operation.
This means that post_notification() can be writing to the pipe whilst a
userspace-invoked operation is holding the pipe mutex and is also doing
something to the ring.
David
next prev parent reply other threads:[~2019-11-08 6:43 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-07 13:35 [RFC PATCH 00/14] pipe: Keyrings, Block and USB notifications [ver #2] David Howells
2019-11-07 13:35 ` [RFC PATCH 01/14] uapi: General notification queue definitions " David Howells
2019-11-07 13:35 ` [RFC PATCH 02/14] security: Add hooks to rule on setting a watch " David Howells
2019-11-07 13:35 ` [RFC PATCH 03/14] security: Add a hook for the point of notification insertion " David Howells
2019-11-07 13:35 ` [RFC PATCH 04/14] pipe: Add O_NOTIFICATION_PIPE " David Howells
2019-11-07 18:16 ` Andy Lutomirski
2019-11-07 18:48 ` David Howells
2019-11-08 5:06 ` Andy Lutomirski
2019-11-08 6:42 ` David Howells [this message]
2019-11-07 13:36 ` [RFC PATCH 05/14] pipe: Add general notification queue support " David Howells
2019-11-07 13:36 ` [RFC PATCH 06/14] keys: Add a notification facility " David Howells
2019-11-07 13:36 ` [RFC PATCH 07/14] Add sample notification program " David Howells
2019-11-07 13:36 ` [RFC PATCH 08/14] pipe: Allow buffers to be marked read-whole-or-error for notifications " David Howells
2019-11-07 18:15 ` Andy Lutomirski
2019-11-07 18:23 ` David Howells
2019-11-07 13:36 ` [RFC PATCH 09/14] pipe: Add notification lossage handling " David Howells
2019-11-07 13:36 ` [RFC PATCH 10/14] Add a general, global device notification watch list " David Howells
2019-11-07 13:37 ` [RFC PATCH 11/14] block: Add block layer notifications " David Howells
2019-11-07 13:37 ` [RFC PATCH 12/14] usb: Add USB subsystem " David Howells
2019-11-07 13:37 ` [RFC PATCH 13/14] selinux: Implement the watch_key security hook " David Howells
2019-11-07 13:37 ` [RFC PATCH 14/14] smack: Implement the watch_key and post_notification hooks " David Howells
2019-11-07 17:16 ` [RFC PATCH 05/14] pipe: Add general notification queue support " David Howells
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