> -----Original Message----- > From: Peter Zijlstra [mailto:pet...@infradead.org] > Sent: Wednesday, January 18, 2017 9:08 PM > To: Byungchul Park > Cc: Boqun Feng; mi...@kernel.org; t...@linutronix.de; wal...@google.com; > kir...@shutemov.name; linux-kernel@vger.kernel.org; linux...@kvack.org; > iamjoonsoo....@lge.com; a...@linux-foundation.org; npig...@gmail.com > Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation > > On Wed, Jan 18, 2017 at 08:54:28PM +0900, Byungchul Park wrote: > > On Wed, Jan 18, 2017 at 12:03:17PM +0100, Peter Zijlstra wrote: > > > 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. > > > > X cannot acquire mutex A because Y already acquired it. > > > > In order words, all statements below mutex_lock A in X cannot run. > > But your timeline shows it does, which is the error that Boqun pointed > out.
I am sorry for not understanding what you are talking about. Do you mean that I should remove all statements below mutex_lock A in X? Or should I move mutex_unlock as Boqun said? What will change?
