Re: waitqueue lockdep annotation

[Jason Baron]

On 11/30/2017 03:50 PM, Andrew Morton wrote:
> On Thu, 30 Nov 2017 06:20:35 -0800 Christoph Hellwig <hch@xxxxxx> wrote:
> 
>> Hi all,
>>
>> this series adds a strategic lockdep_assert_held to __wake_up_common
>> to ensure callers really do hold the wait_queue_head lock when calling
>> the unlocked wake_up variants.  It turns out epoll did not do this
>> for a fairly common path (hit all the time by systemd during bootup),
>> so the second patch fixed this instance as well.
> 
> What are the runtime effects of the epoll bug?
> 

I don't think there is a bug here. The 'wake_up_locked()' calls in epoll
are being protected by the ep->lock, not the wait_queue_head lock. So
arguably the 'annotation' is wrong, but I don't think there is a bug
beyond that.

Thanks,

-Jason