From: Gregory Haskins <ghaskins@novell.com>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: mst@redhat.com, kvm@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
avi@redhat.com, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions
Date: Mon, 22 Jun 2009 12:05:45 -0400 [thread overview]
Message-ID: <4A3FABD9.7080108@novell.com> (raw)
In-Reply-To: <alpine.DEB.1.10.0906211613200.8816@makko.or.mcafeemobile.com>
[-- Attachment #1: Type: text/plain, Size: 2309 bytes --]
Davide Libenzi wrote:
> On Sun, 21 Jun 2009, Gregory Haskins wrote:
>
>
>> This looks great, Davide. I am fairly certain I can now solve the races
>> and even implement Michael's DEASSIGN feature with this patch in place.
>> I will actually fire it up tomorrow when I am back in the office and
>> give it a spin, but I do not spy any more races via visual inspection.
>>
>> Kind Regards,
>> -Greg
>>
>> PS: I was wrong with my previous statement about requiring an embeddable
>> object (eventfd_notifier for me, eventfd_pollcb for you). I think you
>> can technically solve this issue minimally by merely locking the POLLHUP
>> and exposing the kref. However, I think that leads to an more awkward
>> interface (e.g. we already have eventfd_fget() plus we add a new one
>> like eventfd_refget(), which might confuse users), so I prefer what you
>> did here. Just thought I would throw that out there in case you would
>> prefer to change even fewer lines.
>>
>
> I actually ended up exposing the eventfd context anyway, since IMO is a
> better option instead of holding references to the eventfd file (that
> makes VFS people uneasy).
>
I liked "version - 1" better ;)
I think ultimately we still want to hold the fget() for
eventfd_signal(), as it is the producer side. Without it, we have no
way of knowing when the last producer goes away if they happen to be an
in-kernel user.
Also, thinking about it some more, I think I like the non-wrapped pollcb
variant better now. This is because I can uhook the wqh in the POLLHUP
and defer the kref_put() until later. I think this combination gives me
the most ideal environment (even though technically I should not expect
more activity on the wait-queue after the POLLHUP).
In either case, I whipped up a super-lite patch with just the bare
minimum and then developed the KVM solution on top. Things look really
good, now, and I am happy with the result. As an aside, it only has the
following impact on the eventfd core:
fs/eventfd.c | 43 ++++++++++++++++++++++++++++++++++++-------
include/linux/eventfd.h | 7 +++++++
2 files changed, 43 insertions(+), 7 deletions(-)
Ill post the series, including the KVM portions, for review.
Thanks Davide,
-Greg
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 266 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Gregory Haskins <ghaskins@novell.com>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: mst@redhat.com, kvm@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
avi@redhat.com, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions
Date: Mon, 22 Jun 2009 12:05:45 -0400 [thread overview]
Message-ID: <4A3FABD9.7080108@novell.com> (raw)
In-Reply-To: <alpine.DEB.1.10.0906211613200.8816@makko.or.mcafeemobile.com>
[-- Attachment #1: Type: text/plain, Size: 2309 bytes --]
Davide Libenzi wrote:
> On Sun, 21 Jun 2009, Gregory Haskins wrote:
>
>
>> This looks great, Davide. I am fairly certain I can now solve the races
>> and even implement Michael's DEASSIGN feature with this patch in place.
>> I will actually fire it up tomorrow when I am back in the office and
>> give it a spin, but I do not spy any more races via visual inspection.
>>
>> Kind Regards,
>> -Greg
>>
>> PS: I was wrong with my previous statement about requiring an embeddable
>> object (eventfd_notifier for me, eventfd_pollcb for you). I think you
>> can technically solve this issue minimally by merely locking the POLLHUP
>> and exposing the kref. However, I think that leads to an more awkward
>> interface (e.g. we already have eventfd_fget() plus we add a new one
>> like eventfd_refget(), which might confuse users), so I prefer what you
>> did here. Just thought I would throw that out there in case you would
>> prefer to change even fewer lines.
>>
>
> I actually ended up exposing the eventfd context anyway, since IMO is a
> better option instead of holding references to the eventfd file (that
> makes VFS people uneasy).
>
I liked "version - 1" better ;)
I think ultimately we still want to hold the fget() for
eventfd_signal(), as it is the producer side. Without it, we have no
way of knowing when the last producer goes away if they happen to be an
in-kernel user.
Also, thinking about it some more, I think I like the non-wrapped pollcb
variant better now. This is because I can uhook the wqh in the POLLHUP
and defer the kref_put() until later. I think this combination gives me
the most ideal environment (even though technically I should not expect
more activity on the wait-queue after the POLLHUP).
In either case, I whipped up a super-lite patch with just the bare
minimum and then developed the KVM solution on top. Things look really
good, now, and I am happy with the result. As an aside, it only has the
following impact on the eventfd core:
fs/eventfd.c | 43 ++++++++++++++++++++++++++++++++++++-------
include/linux/eventfd.h | 7 +++++++
2 files changed, 43 insertions(+), 7 deletions(-)
Ill post the series, including the KVM portions, for review.
Thanks Davide,
-Greg
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 266 bytes --]
next prev parent reply other threads:[~2009-06-22 16:07 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-16 2:29 [KVM-RFC PATCH 0/2] eventfd enhancements for irqfd/iosignalfd Gregory Haskins
2009-06-16 2:29 ` [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface Gregory Haskins
2009-06-16 14:02 ` Michael S. Tsirkin
2009-06-16 14:11 ` Gregory Haskins
2009-06-16 14:38 ` Michael S. Tsirkin
2009-06-16 14:48 ` Gregory Haskins
2009-06-16 14:54 ` Gregory Haskins
2009-06-16 15:16 ` Michael S. Tsirkin
2009-06-16 14:55 ` Michael S. Tsirkin
2009-06-16 15:20 ` Gregory Haskins
2009-06-16 15:41 ` Michael S. Tsirkin
2009-06-16 16:17 ` Gregory Haskins
2009-06-16 16:19 ` Davide Libenzi
2009-06-16 17:01 ` Gregory Haskins
2009-06-17 16:38 ` Davide Libenzi
2009-06-17 17:28 ` Gregory Haskins
2009-06-17 17:44 ` Davide Libenzi
2009-06-17 19:17 ` Gregory Haskins
2009-06-17 19:50 ` Davide Libenzi
2009-06-17 21:48 ` Gregory Haskins
2009-06-17 23:21 ` Davide Libenzi
2009-06-18 6:23 ` Michael S. Tsirkin
2009-06-18 17:52 ` Davide Libenzi
2009-06-18 14:01 ` Gregory Haskins
2009-06-18 14:01 ` Gregory Haskins
2009-06-18 17:44 ` Davide Libenzi
2009-06-18 19:04 ` Gregory Haskins
2009-06-18 19:04 ` Gregory Haskins
2009-06-18 22:03 ` Davide Libenzi
2009-06-18 22:47 ` Gregory Haskins
2009-06-18 22:47 ` Gregory Haskins
2009-06-19 18:51 ` Gregory Haskins
2009-06-19 18:51 ` [PATCH 1/3] eventfd: Allow waiters to be notified about the eventfd file* going away Gregory Haskins
2009-06-19 18:51 ` [PATCH 2/3] eventfd: add generalized notifier interface Gregory Haskins
2009-06-19 18:51 ` [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions Gregory Haskins
2009-06-19 19:10 ` Davide Libenzi
2009-06-19 21:16 ` Gregory Haskins
2009-06-19 21:26 ` Davide Libenzi
2009-06-19 21:49 ` Gregory Haskins
2009-06-19 21:54 ` Davide Libenzi
2009-06-19 22:47 ` Davide Libenzi
2009-06-20 2:09 ` Gregory Haskins
2009-06-20 21:17 ` Davide Libenzi
2009-06-20 22:11 ` Davide Libenzi
2009-06-20 23:48 ` Davide Libenzi
2009-06-21 1:14 ` Gregory Haskins
2009-06-21 16:51 ` Davide Libenzi
2009-06-21 18:39 ` Gregory Haskins
2009-06-21 23:54 ` Davide Libenzi
2009-06-22 16:05 ` Gregory Haskins [this message]
2009-06-22 16:05 ` Gregory Haskins
2009-06-22 17:01 ` Davide Libenzi
2009-06-22 17:43 ` Gregory Haskins
2009-06-22 17:43 ` Gregory Haskins
2009-06-22 18:03 ` Davide Libenzi
2009-06-22 18:31 ` Gregory Haskins
2009-06-22 18:31 ` Gregory Haskins
2009-06-22 18:40 ` Davide Libenzi
2009-06-22 18:41 ` Michael S. Tsirkin
2009-06-22 18:51 ` Davide Libenzi
2009-06-22 19:05 ` Michael S. Tsirkin
2009-06-22 19:26 ` Gregory Haskins
2009-06-22 19:29 ` Davide Libenzi
2009-06-22 20:06 ` Gregory Haskins
2009-06-22 22:53 ` Davide Libenzi
2009-06-23 1:03 ` Gregory Haskins
2009-06-23 1:17 ` Davide Libenzi
2009-06-23 1:26 ` Gregory Haskins
2009-06-23 1:26 ` Gregory Haskins
2009-06-23 14:29 ` Davide Libenzi
2009-06-23 14:37 ` Gregory Haskins
2009-06-23 14:37 ` Gregory Haskins
2009-06-23 14:35 ` Davide Libenzi
2009-06-23 14:42 ` Gregory Haskins
2009-06-23 14:42 ` Gregory Haskins
2009-06-23 15:04 ` Michael S. Tsirkin
2009-06-22 20:28 ` Michael S. Tsirkin
2009-06-22 19:16 ` Gregory Haskins
2009-06-22 19:54 ` Davide Libenzi
2009-06-24 3:25 ` Rusty Russell
2009-06-24 22:45 ` Davide Libenzi
2009-06-25 11:42 ` Rusty Russell
2009-06-25 16:34 ` Davide Libenzi
2009-06-25 17:32 ` Gregory Haskins
2009-06-25 18:26 ` Michael S. Tsirkin
2009-06-25 18:41 ` Gregory Haskins
2009-06-26 11:23 ` Michael S. Tsirkin
2009-06-23 3:25 ` Rusty Russell
2009-06-23 14:31 ` Davide Libenzi
2009-06-25 0:19 ` Davide Libenzi
2009-06-21 1:05 ` Gregory Haskins
2009-06-16 17:54 ` [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface Michael S. Tsirkin
2009-06-16 18:09 ` Gregory Haskins
2009-06-17 14:45 ` Michael S. Tsirkin
2009-06-17 15:02 ` Gregory Haskins
2009-06-17 16:25 ` Michael S. Tsirkin
2009-06-17 16:41 ` Gregory Haskins
2009-06-16 14:17 ` Gregory Haskins
2009-06-16 14:22 ` Gregory Haskins
2009-06-16 14:40 ` Gregory Haskins
2009-06-16 14:46 ` Michael S. Tsirkin
2009-06-18 9:03 ` Avi Kivity
2009-06-18 11:43 ` Gregory Haskins
2009-06-16 2:30 ` [KVM-RFC PATCH 2/2] eventfd: add module reference counting support for registered notifiers Gregory Haskins
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=4A3FABD9.7080108@novell.com \
--to=ghaskins@novell.com \
--cc=avi@redhat.com \
--cc=davidel@xmailserver.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=mst@redhat.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=rusty@rustcorp.com.au \
/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.