Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation

[Peter Zijlstra]

On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote:
> On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote:
> > On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote:
> > [...]
> > > +Example 1:
> > > +
> > > +   CONTEXT X		   CONTEXT Y
> > > +   ---------		   ---------
> > > +   mutext_lock A
> > > +			   lock_page B
> > > +   lock_page B
> > > +			   mutext_lock A /* DEADLOCK */
> > 
> > s/mutext_lock/mutex_lock
> 
> Thank you.
> 
> > > +Example 3:
> > > +
> > > +   CONTEXT X		   CONTEXT Y
> > > +   ---------		   ---------
> > > +			   mutex_lock A
> > > +   mutex_lock A
> > > +   mutex_unlock A
> > > +			   wait_for_complete B /* DEADLOCK */
> > 
> > I think this part better be:
> > 
> >    CONTEXT X		   CONTEXT Y
> >    ---------		   ---------
> >    			   mutex_lock A
> >    mutex_lock A
> >    			   wait_for_complete B /* DEADLOCK */
> >    mutex_unlock A
> > 
> > , right? Because Y triggers DEADLOCK before X could run mutex_unlock().
> 
> There's no different between two examples.

There is..

> No matter which one is chosen, mutex_lock A in CONTEXT X cannot be passed.

But your version shows it does mutex_unlock() before CONTEXT Y does
wait_for_completion().

The thing about these diagrams is that both columns are assumed to have
the same timeline.