On Fri, May 06, 2022 at 09:11:35AM +0900, Byungchul Park wrote: > Linus wrote: > > > > On Wed, May 4, 2022 at 1:19 AM Byungchul Park <byungchul.p...@lge.com> > > wrote: > > > > > > Hi Linus and folks, > > > > > > I've been developing a tool for detecting deadlock possibilities by > > > tracking wait/event rather than lock(?) acquisition order to try to > > > cover all synchonization machanisms. > > > > So what is the actual status of reports these days? > > > > Last time I looked at some reports, it gave a lot of false positives > > due to mis-understanding prepare_to_sleep(). > > Yes, it was. I handled the case in the following way: > > 1. Stage the wait at prepare_to_sleep(), which might be used at commit. > Which has yet to be an actual wait that Dept considers. > 2. If the condition for sleep is true, the wait will be committed at > __schedule(). The wait becomes an actual one that Dept considers. > 3. If the condition is false and the task gets back to TASK_RUNNING, > clean(=reset) the staged wait. > > That way, Dept only works with what actually hits to __schedule() for > the waits through sleep. > > > For this all to make sense, it would need to not have false positives > > (or at least a very small number of them together with a way to sanely > > Yes. I agree with you. I got rid of them that way I described above. >
IMHO DEPT should not report what lockdep allows (Not talking about wait events). I mean lockdep allows some kind of nested locks but DEPT reports them. When I was collecting reports from DEPT on varous configurations, Most of them was report of down_write_nested(), which is allowed in lockdep. DEPT should not report at least what we know it's not a real deadlock. Otherwise there will be reports that is never fixed, which is quite unpleasant and reporters cannot examine all of them if it's real deadlock or not. > > get rid of them), and also have a track record of finding things that > > lockdep doesn't. > > I have some reports that wait_for_completion or waitqueue is involved. > It's worth noting those are not tracked by Lockdep. I'm checking if > those are true positive or not. I will share those reports once I get > more convinced for that. > > > Maybe such reports have been sent out with the current situation, and > > I haven't seen them. > > Dept reports usually have been sent to me privately, not in LKML. As I > told you, I'm planning to share them. > > Byungchul > > > > > Linus > > -- Thanks, Hyeonggon
