Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu()

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Mar 06, 2012 at 11:47:25AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote:
> > o       The srcu callback is new thing, I hope it is completely preemptible,
> >         even sleepable. It does in this implemetation, I use work_struct
> >         to stand for every srcu callback. 
> 
> I didn't need the callbacks to sleep too, I just needed the read-side
> srcu bit.
> 
> There's an argument against making the callbacks able to sleep like that
> in that you typically want to minimize the amount of work done in the
> callbacks, allowing them to sleep invites to callbacks that do _way_ too
> much work.
> 
> I haven't made my mind up if I care yet.. :-)

I prefer that they don't sleep.  Easy to push anything that needs to
sleep off to a work queue.  And allowing sleeping in an SRCU callback
function sounds like something that could cause serious problems down
the road.