From: "Michael S. Tsirkin" <mst@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Davide Libenzi <davidel@xmailserver.org>,
mtosatti@redhat.com, kvm@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove
Date: Thu, 21 Jan 2010 20:02:50 +0200 [thread overview]
Message-ID: <20100121180250.GJ16707@redhat.com> (raw)
In-Reply-To: <4B589582.9030300@redhat.com>
On Thu, Jan 21, 2010 at 07:57:22PM +0200, Avi Kivity wrote:
> On 01/21/2010 07:56 PM, Avi Kivity wrote:
>> On 01/21/2010 07:45 PM, Michael S. Tsirkin wrote:
>>>
>>>> But you're in process context. An eventfd never blocks.
>>> Yes it blocks if counter is 0. And we don't know
>>> it's not 0 unless we read :) catch-22.
>>
>> Ah yes, I forgot.
>>
>
> Well, you can poll it and then read it... this introduces a new race (if
> userspace does a read in parallel) but it's limited to kvm and buggy
> userspace.
I would rather not require that userspace never reads this fd.
You are right that it does not now, but adding this as requirement
looks like exporting an implementation bug to userspace.
--
MST
next prev parent reply other threads:[~2010-01-21 18:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-21 16:26 [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove Michael S. Tsirkin
2010-01-21 16:58 ` Davide Libenzi
2010-01-21 17:13 ` Avi Kivity
2010-01-21 17:14 ` Avi Kivity
2010-01-21 17:23 ` Michael S. Tsirkin
2010-01-21 17:33 ` Avi Kivity
2010-01-21 17:32 ` Michael S. Tsirkin
2010-01-21 17:47 ` Avi Kivity
2010-01-21 17:45 ` Michael S. Tsirkin
2010-01-21 17:56 ` Avi Kivity
2010-01-21 17:57 ` Avi Kivity
2010-01-21 18:02 ` Michael S. Tsirkin [this message]
2010-01-24 11:06 ` Avi Kivity
2010-01-21 17:50 ` Davide Libenzi
2010-01-21 17:50 ` Michael S. Tsirkin
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