Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12

[Peter Zijlstra]

On Wed, Apr 19, 2017 at 01:28:45PM +0200, Peter Zijlstra wrote:
> 
> So the thing Maz complained about is because KVM assumes
> synchronize_srcu() is 'free' when there is no srcu_read_lock() activity.
> This series 'breaks' that.


Could've been call_srcu() instead. Looking at the code that triggers the
sp->running case and we slow down. That is !running will queue and
insta-complete the callback, resulting in done=true and no waiting.

> 
> I've not looked hard enough at the new SRCU to see if its possible to
> re-instate that feature.