Messages in this thread | | | Date | Tue, 5 Sep 2017 11:36:24 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation |
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On Tue, Sep 05, 2017 at 05:57:27PM +0900, Byungchul Park wrote: > On Tue, Sep 05, 2017 at 09:19:30AM +0200, Peter Zijlstra wrote: > > On Tue, Sep 05, 2017 at 09:08:25AM +0200, Peter Zijlstra wrote: > > > So you worry about max_active==1 ? Or you worry about pool->lock or > > > about the thread setup? I'm still not sure. > > > > So the thing about pool->lock is that its a leaf lock, we take nothing > > I think the following sentence is a key, I hope... > > Leaf locks can also create dependecies with *crosslocks*. These > dependencies are not built between holding locks like typical locks.
They can create dependencies, but they _cannot_ create deadlocks. So there's no value in those dependencies.
> > And the whole setup stuff isn't properly preserved between works in any > > case, only the first few works would ever see that history, so why > > bother. > > As I said in another reply, what about (1), (3) and (5) in my example?
So for single-threaded workqueues, I'd like to get recursive-read sorted and then we can make the lockdep_invariant_state() conditional.
Using recurisve-read lock for the wq lockdep_map's has the same effect as your might thing without having to introduce new magic.
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