From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, Ray Strode <rstrode@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Steven Whitehouse <swhiteho@redhat.com>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
raven@themaw.net, keyrings@vger.kernel.org,
linux-usb@vger.kernel.org,
linux-block <linux-block@vger.kernel.org>,
Christian Brauner <christian@brauner.io>,
LSM List <linux-security-module@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Ray, Debarshi" <debarshi.ray@gmail.com>,
Robbie Harwood <rharwood@redhat.com>
Subject: Re: Why add the general notification queue and its sources
Date: Fri, 06 Sep 2019 11:09:17 +0100 [thread overview]
Message-ID: <27732.1567764557@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHk-=wjt2Eb+yEDOcQwCa0SrZ4cWu967OtQG8Vz21c=n5ZP1Nw@mail.gmail.com>
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> But it's *literally* just finding the places that work with
> pipe->curbuf/nrbufs and making them use atomic updates.
No. It really isn't. That's two variables that describe the occupied section
of the buffer. Unless you have something like a 68020 with CAS2, or put them
next to each other so you can use CMPXCHG8, you can't do that.
They need converting to head/tail pointers first.
> They really would work with almost anything. You could even mix-and-match
> "data generated by kernel" and "data done by 'write()' or 'splice()' by a
> user process".
Imagine that userspace writes a large message and takes the mutex. At the
same time something in softirq context decides *it* wants to write a message -
it can't take the mutex and it can't wait, so the userspace write would have
to cause the kernel message to be dropped.
What I would have to do is make a write to a notification pipe go through
post_notification() and limit the size to the maximum for a single message.
Much easier to simply suppress writes and splices on pipes that have been set
up to be notification queues - at least for now.
David
WARNING: multiple messages have this Message-ID (diff)
From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, Ray Strode <rstrode@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Steven Whitehouse <swhiteho@redhat.com>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
raven@themaw.net, keyrings@vger.kernel.org,
linux-usb@vger.kernel.org,
linux-block <linux-block@vger.kernel.org>,
Christian Brauner <christian@brauner.io>,
LSM List <linux-security-module@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Ray, Debarshi" <debarshi.ray@gmail.com>,
Robbie Harwood <rharwood@redhat.com>
Subject: Re: Why add the general notification queue and its sources
Date: Fri, 06 Sep 2019 10:09:17 +0000 [thread overview]
Message-ID: <27732.1567764557@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHk-=wjt2Eb+yEDOcQwCa0SrZ4cWu967OtQG8Vz21c=n5ZP1Nw@mail.gmail.com>
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> But it's *literally* just finding the places that work with
> pipe->curbuf/nrbufs and making them use atomic updates.
No. It really isn't. That's two variables that describe the occupied section
of the buffer. Unless you have something like a 68020 with CAS2, or put them
next to each other so you can use CMPXCHG8, you can't do that.
They need converting to head/tail pointers first.
> They really would work with almost anything. You could even mix-and-match
> "data generated by kernel" and "data done by 'write()' or 'splice()' by a
> user process".
Imagine that userspace writes a large message and takes the mutex. At the
same time something in softirq context decides *it* wants to write a message -
it can't take the mutex and it can't wait, so the userspace write would have
to cause the kernel message to be dropped.
What I would have to do is make a write to a notification pipe go through
post_notification() and limit the size to the maximum for a single message.
Much easier to simply suppress writes and splices on pipes that have been set
up to be notification queues - at least for now.
David
next prev parent reply other threads:[~2019-09-06 10:09 UTC|newest]
Thread overview: 234+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-04 22:15 [PATCH 00/11] Keyrings, Block and USB notifications [ver #8] David Howells
2019-09-04 22:15 ` David Howells
2019-09-04 22:15 ` David Howells
2019-09-04 22:15 ` [PATCH 01/11] uapi: General notification ring definitions " David Howells
2019-09-04 22:15 ` David Howells
2019-09-04 22:15 ` David Howells
2019-09-04 22:16 ` [PATCH 02/11] security: Add hooks to rule on setting a watch " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 03/11] security: Add a hook for the point of notification insertion " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 04/11] General notification queue with user mmap()'able ring buffer " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 05/11] keys: Add a notification facility " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 06/11] Add a general, global device notification watch list " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 07/11] block: Add block layer notifications " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` [PATCH 08/11] usb: Add USB subsystem " David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:16 ` David Howells
2019-09-04 22:17 ` [PATCH 09/11] Add sample notification program " David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:17 ` [PATCH 10/11] selinux: Implement the watch_key security hook " David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:17 ` [PATCH 11/11] smack: Implement the watch_key and post_notification hooks " David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:17 ` David Howells
2019-09-04 22:28 ` [PATCH 00/11] Keyrings, Block and USB notifications " Linus Torvalds
2019-09-04 22:28 ` Linus Torvalds
2019-09-05 17:01 ` Why add the general notification queue and its sources David Howells
2019-09-05 17:01 ` David Howells
2019-09-05 17:19 ` Linus Torvalds
2019-09-05 17:19 ` Linus Torvalds
2019-09-05 18:32 ` Ray Strode
2019-09-05 18:32 ` Ray Strode
2019-09-05 18:32 ` Ray Strode
2019-09-05 20:39 ` Linus Torvalds
2019-09-05 20:39 ` Linus Torvalds
2019-09-06 19:32 ` Ray Strode
2019-09-06 19:32 ` Ray Strode
2019-09-06 19:41 ` Ray Strode
2019-09-06 19:41 ` Ray Strode
2019-09-06 19:53 ` Robbie Harwood
2019-09-06 19:53 ` Robbie Harwood
2019-09-06 19:53 ` Robbie Harwood
2019-09-05 21:32 ` David Howells
2019-09-05 21:32 ` David Howells
2019-09-05 22:08 ` Linus Torvalds
2019-09-05 22:08 ` Linus Torvalds
2019-09-05 23:18 ` David Howells
2019-09-05 23:18 ` David Howells
2019-09-06 0:07 ` Linus Torvalds
2019-09-06 0:07 ` Linus Torvalds
2019-09-06 10:09 ` David Howells [this message]
2019-09-06 10:09 ` David Howells
2019-09-06 15:35 ` Linus Torvalds
2019-09-06 15:35 ` Linus Torvalds
2019-09-06 15:53 ` Linus Torvalds
2019-09-06 15:53 ` Linus Torvalds
2019-09-06 16:12 ` Steven Whitehouse
2019-09-06 16:12 ` Steven Whitehouse
2019-09-06 17:07 ` Linus Torvalds
2019-09-06 17:07 ` Linus Torvalds
2019-09-06 17:14 ` Linus Torvalds
2019-09-06 17:14 ` Linus Torvalds
2019-09-06 21:19 ` David Howells
2019-09-06 21:19 ` David Howells
2019-09-06 17:14 ` Andy Lutomirski
2019-09-06 17:14 ` Andy Lutomirski
2019-09-05 18:37 ` Steven Whitehouse
2019-09-05 18:37 ` Steven Whitehouse
2019-09-05 18:51 ` Ray Strode
2019-09-05 18:51 ` Ray Strode
2019-09-05 20:09 ` David Lehman
2019-09-05 20:09 ` David Lehman
2019-09-05 18:33 ` Greg Kroah-Hartman
2019-09-05 18:33 ` Greg Kroah-Hartman
[not found] <20190903085706.7700-1-hdanton@sina.com>
2019-08-30 13:57 ` [PATCH 00/11] Keyrings, Block and USB notifications [ver #7] David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` [PATCH 01/11] uapi: General notification ring definitions " David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` [PATCH 02/11] security: Add hooks to rule on setting a watch " David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` [PATCH 03/11] security: Add a hook for the point of notification insertion " David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` [PATCH 04/11] General notification queue with user mmap()'able ring buffer " David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` [PATCH 05/11] keys: Add a notification facility " David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:57 ` David Howells
2019-08-30 13:58 ` [PATCH 06/11] Add a general, global device notification watch list " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-09-03 8:34 ` Yoshihiro Shimoda
2019-09-03 8:34 ` Yoshihiro Shimoda
2019-09-03 8:34 ` Yoshihiro Shimoda
2019-09-03 16:41 ` David Howells
2019-09-03 16:41 ` David Howells
2019-09-03 16:41 ` David Howells
2019-08-30 13:58 ` [PATCH 07/11] block: Add block layer notifications " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` [PATCH 08/11] usb: Add USB subsystem " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-09-03 8:53 ` Yoshihiro Shimoda
2019-09-03 8:53 ` Yoshihiro Shimoda
2019-09-03 8:53 ` Yoshihiro Shimoda
2019-09-03 9:37 ` Greg Kroah-Hartman
2019-09-03 9:37 ` Greg Kroah-Hartman
2019-09-03 9:37 ` Greg Kroah-Hartman
2019-09-04 1:53 ` Yoshihiro Shimoda
2019-09-04 1:53 ` Yoshihiro Shimoda
2019-09-04 1:53 ` Yoshihiro Shimoda
2019-09-03 12:51 ` Guenter Roeck
2019-09-03 12:51 ` Guenter Roeck
2019-09-03 16:07 ` David Howells
2019-09-03 16:07 ` David Howells
2019-09-03 16:12 ` Guenter Roeck
2019-09-03 16:12 ` Guenter Roeck
2019-09-03 16:29 ` David Howells
2019-09-03 16:29 ` David Howells
2019-09-03 17:06 ` Alan Stern
2019-09-03 17:06 ` Alan Stern
2019-09-03 17:06 ` Alan Stern
2019-09-03 17:17 ` Alan Stern
2019-09-03 17:17 ` Alan Stern
2019-09-03 17:17 ` Alan Stern
2019-09-04 15:17 ` David Howells
2019-09-04 15:17 ` David Howells
2019-08-30 13:58 ` [PATCH 09/11] Add sample notification program " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` [PATCH 10/11] selinux: Implement the watch_key security hook " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 14:15 ` Stephen Smalley
2019-08-30 14:15 ` Stephen Smalley
2019-08-30 14:23 ` David Howells
2019-08-30 14:23 ` David Howells
2019-08-30 14:41 ` David Howells
2019-08-30 14:41 ` David Howells
2019-08-30 15:41 ` Stephen Smalley
2019-08-30 15:41 ` Stephen Smalley
2019-08-30 13:58 ` [PATCH 11/11] smack: Implement the watch_key and post_notification hooks [untested] " David Howells
2019-08-30 13:58 ` David Howells
2019-08-30 13:58 ` David Howells
2019-09-03 15:20 ` Casey Schaufler
2019-09-03 15:20 ` Casey Schaufler
2019-09-03 15:41 ` David Howells
2019-09-03 15:41 ` David Howells
2019-09-03 17:40 ` Casey Schaufler
2019-09-03 17:40 ` Casey Schaufler
2019-09-03 18:06 ` David Howells
2019-09-03 18:06 ` David Howells
2019-09-03 22:16 ` Casey Schaufler
2019-09-03 22:16 ` Casey Schaufler
2019-09-03 22:39 ` David Howells
2019-09-03 22:39 ` David Howells
2019-09-04 12:08 ` David Howells
2019-09-04 12:08 ` David Howells
2019-09-04 14:56 ` Casey Schaufler
2019-09-04 14:56 ` Casey Schaufler
2019-08-30 14:15 ` watch_queue(7) manpage David Howells
2019-08-30 14:15 ` David Howells
2019-08-30 14:15 ` David Howells
2019-08-30 14:15 ` watch_devices(2) manpage David Howells
2019-08-30 14:15 ` David Howells
2019-08-30 14:16 ` keyctl_watch_key.3 manpage David Howells
2019-08-30 14:16 ` David Howells
2019-08-30 22:09 ` [PATCH 00/11] Keyrings, Block and USB notifications [ver #7] Casey Schaufler
2019-08-30 22:09 ` Casey Schaufler
2019-09-02 12:39 ` David Howells
2019-09-02 12:39 ` David Howells
2019-09-02 13:26 ` David Howells
2019-09-02 13:26 ` David Howells
2019-09-03 16:06 ` [PATCH 04/11] General notification queue with user mmap()'able ring buffer " David Howells
2019-09-03 16:06 ` David Howells
2019-09-03 16:37 ` David Howells
2019-09-03 16:37 ` David Howells
-- strict thread matches above, loose matches on Subject: below --
2019-08-29 18:29 [PATCH 00/11] Keyrings, Block and USB notifications [ver #6] David Howells
2019-08-29 18:29 ` David Howells
2019-08-29 18:29 ` David Howells
2019-08-29 18:29 ` [PATCH 01/11] uapi: General notification ring definitions " David Howells
2019-08-29 18:29 ` David Howells
2019-08-29 18:29 ` David Howells
2019-08-29 18:30 ` [PATCH 02/11] security: Add hooks to rule on setting a watch " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` [PATCH 03/11] security: Add a hook for the point of notification insertion " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` [PATCH 04/11] General notification queue with user mmap()'able ring buffer " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` [PATCH 05/11] keys: Add a notification facility " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` [PATCH 06/11] Add a general, global device notification watch list " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` [PATCH 07/11] block: Add block layer notifications " David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:30 ` David Howells
2019-08-29 18:31 ` [PATCH 08/11] usb: Add USB subsystem " David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` [PATCH 09/11] Add sample notification program " David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` [PATCH 10/11] selinux: Implement the watch_key security hook " David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:44 ` Stephen Smalley
2019-08-29 18:44 ` Stephen Smalley
2019-08-29 19:11 ` David Howells
2019-08-29 19:11 ` David Howells
2019-08-29 18:31 ` [PATCH 11/11] smack: Implement the watch_key and post_notification hooks [untested] " David Howells
2019-08-29 18:31 ` David Howells
2019-08-29 18:31 ` David Howells
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