On Wed, Aug 23, 2017 at 11:31:18AM +0900, Byungchul Park wrote: > On Tue, Aug 22, 2017 at 11:06:03AM +0200, Peter Zijlstra wrote:
> Currently, we do the following in process_one_work(), > > lockdep_map_acquire for a workqueue > lockdep_map_acquire for a work > > But IMHO it should be, > > lockdep_map_acquire for a pair of workqueue and work. > > Right? No, it is right. We need the two 'locks'. The work one is for flush_work(), the workqueue one is for flush_workqueue(). Just like how flush_work() must not depend on any lock taken inside the work, flush_workqueue() callers must not hold any lock acquired inside any work ran inside the workqueue. This cannot be done with a single 'lock'. The reason flush_work() also depends on the wq 'lock' is because doing flush_work() from inside work is a possible problem for single threaded workqueues and workqueues with a rescuer. > > Agreed. The interaction with workqueues is buggered. > > I think original uses of lockdep_map were already wrong. I mean it's > not a problem of newly introduced code. Not wrong per-se, the new code certainly places more constraints on it.
