From: Avi Kivity <avi@redhat.com>
To: "Michael S. Tsirkin" <mst@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 19:57:22 +0200 [thread overview]
Message-ID: <4B589582.9030300@redhat.com> (raw)
In-Reply-To: <4B589532.9070408@redhat.com>
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.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2010-01-21 17:57 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 [this message]
2010-01-21 18:02 ` Michael S. Tsirkin
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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