Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE_LOCKING

[Byungchul Park]

On Mon, Aug 21, 2017 at 05:46:00PM +0200, Peter Zijlstra wrote:
> Now given the above observance rule and the fact that the below report
> is from the complete, the thing that happened appears to be:
> 
> 
> 	lockdep_map_acquire(&work->lockdep_map)
> 	down_write(&A)
> 
> 			down_write(&A)
> 			wait_for_completion(&C)
> 
> 					lockdep_map_acquire(&work_lockdep_map);
> 					complete(&C)
> 
> Which lockdep then puked over because both sides saw the same work
> class.
> 
> Byungchul; should we not exclude the work class itself, it appears to me
> the workqueue code is explicitly parallel, or am I confused again?

Do you mean the lockdep_map_acquire(&work->lockdep_map) used manuallly?

That was introduced by Johannes:

commit 4e6045f134784f4b158b3c0f7a282b04bd816887
"workqueue: debug flushing deadlocks with lockdep"

I am not sure but, for that purpose, IMHO, we can use a
lockdep_map_acquire_read() instead, in process_one_work(), can't we?