Re: [RFC PATCH v4 01/13] ktask: add documentation

[Daniel Jordan]

On Wed, Nov 07, 2018 at 11:27:52AM +0100, Peter Zijlstra wrote:
> On Tue, Nov 06, 2018 at 08:51:54PM +0000, Jason Gunthorpe wrote:
> > On Tue, Nov 06, 2018 at 12:34:11PM -0800, Daniel Jordan wrote:
> > 
> > > > What isn't clear is if this calling thread is waiting or not. Only do
> > > > this inheritance trick if it is actually waiting on the work. If it is
> > > > not, nobody cares.
> > > 
> > > The calling thread waits.  Even if it didn't though, the inheritance trick
> > > would still be desirable for timely completion of the job.
> > 
> > Can you make lockdep aware that this is synchronous?
> > 
> > ie if I do
> > 
> >   mutex_lock()
> >   ktask_run()
> >   mutex_lock()
> > 
> > Can lockdep know that all the workers are running under that lock?
> > 
> > I'm thinking particularly about rtnl_lock as a possible case, but
> > there could also make some sense to hold the read side of the mm_sem
> > or similar like the above.
> 
> Yes, the normal trick is adding a fake lock to ktask_run and holding
> that over the actual job. See lock_map* in flush_workqueue() vs
> process_one_work().

I'll add that for the next version.