Messages in this thread | | | Date | Tue, 5 Sep 2017 19:31:44 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation |
| |
On Tue, Sep 05, 2017 at 11:36:24AM +0200, Peter Zijlstra wrote: > 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.
Let me show you a possible scenario with a leaf lock:
lock(A) lock(A) wait_for_completion(B) unlock(A) ... ... unlock(A) process_one_work() work->func() complete(B)
It's a deadlock by a lead lock A and completion B.
> > > 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.
Recursive-read and the hint I proposed(a.k.a. might) should be used for their different specific applications. Both meaning and constraints of them are totally different.
Using a right function semantically is more important than making it just work, as you know. Wrong?
| |