linux-kernel - Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

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Message-ID: <20100121174538.GG16707@redhat.com>
Date:	Thu, 21 Jan 2010 19:45:38 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>, mtosatti@...hat.com,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

On Thu, Jan 21, 2010 at 07:47:40PM +0200, Avi Kivity wrote:
> On 01/21/2010 07:32 PM, Michael S. Tsirkin wrote:
>>
>>> Can't you read from the file?
>>>      
>> IMO no, the read could block.
>>    
>
> 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.

> -- 
> Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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