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

Avi Kivity
2010-01-21T17:57:26Z

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.