linux-kernel - Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE

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Date:   Thu, 24 Aug 2017 16:30:58 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Chinner <david@...morbit.com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Tejun Heo <tj@...nel.org>, Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING

On Thu, Aug 24, 2017 at 11:02:36AM +0900, Byungchul Park wrote:
> On Wed, Aug 23, 2017 at 12:20:48PM +0200, Peter Zijlstra wrote:
> > On Wed, Aug 23, 2017 at 11:12:17AM +0900, Byungchul Park wrote:
> > 
> > > > > We have to detect dependecies if it exists, even in the following case:
> > > > > 
> > > > > oooooooiiiiiiiiiiiiiiiiiii.........
> > > > >   |<- range for commit ->|
> > > > > 
> > > > >   where
> > > > >   o: acquisition outside of each work,
> > > > >   i: acquisition inside of each work,
> > > > > 
> > > > > With yours, we can never detect dependecies wrt 'o'.
> > > > 
> > > > There really shouldn't be any o's when you call
> > > 
> > > There can be any o's.
> > 
> > Yes, but they _must_ be irrelevant, see below.
> 
> No, they can be relevant, see below.

I meant we have to detect problems like, just for example:

A worker:

   acquire(A)
   process_one_work()
      acquire(B)

      crossrelease_hist_start(PROC)
      work_x->func()
         acquire(C)
         release(C)
         complete(D)
      crossrelease_hist_end(PROC)

      release(B)
   release(A)

A task:

   acquire(A)
   acquire(B)
   initiate work_x
   wait_for_completion(D)

In this case, I want to detect a problem by creating true dependencies,
which are:

A -> B
B -> C
D -> A // You are currently trying to invalidate this unnecessarily.
D -> B // You are currently trying to invalidate this unnecessarily.
D -> C

in the worker,

B -> D

in the task.

Crossrelease should detect the problem with the following chain:

A -> B -> D -> A

or

B -> D -> B

So, please keep my original code unchanged conceptially.