On Fri, Mar 04, 2022 at 12:20:02PM +0900, Byungchul Park wrote: > > I found a point that the two wait channels don't lead a deadlock in > some cases thanks to Jan Kara. I will fix it so that Dept won't > complain it. I sent my last (admittedly cranky) message before you sent this. I'm glad you finally understood Jan's explanation. I was trying to tell you the same thing, but apparently I failed to communicate in a sufficiently clear manner. In any case, what Jan described is a fundamental part of how wait queues work, and I'm kind of amazed that you were able to implement DEPT without understanding it. (But maybe that is why some of the DEPT reports were completely incomprehensible to me; I couldn't interpret why in the world DEPT was saying there was a problem.) In any case, the thing I would ask is a little humility. We regularly use lockdep, and we run a huge number of stress tests, throughout each development cycle. So if DEPT is issuing lots of reports about apparently circular dependencies, please try to be open to the thought that the fault is in DEPT, and don't try to argue with maintainers that their code MUST be buggy --- but since you don't understand our code, and DEPT must be theoretically perfect, that it is up to the Maintainers to prove to you that their code is correct. I am going to gently suggest that it is at least as likely, if not more likely, that the failure is in DEPT or your understanding of what how kernel wait channels and locking works. After all, why would it be that we haven't found these problems via our other QA practices? Cheers, - Ted
