On Sat, May 07, 2022 at 04:20:50PM +0900, Hyeonggon Yoo wrote: > 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.park@xxxxxxx> 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 No. > wait events). I mean lockdep allows some kind of nested locks but > DEPT reports them. You have already asked exactly same question in another thread of LKML. That time I answered to it but let me explain it again. --- CASE 1. lock L with depth n lock_nested L' with depth n + 1 ... unlock L' unlock L This case is allowed by Lockdep. This case is allowed by DEPT cuz it's not a deadlock. CASE 2. lock L with depth n lock A lock_nested L' with depth n + 1 ... unlock L' unlock A unlock L This case is allowed by Lockdep. This case is *NOT* allowed by DEPT cuz it's a *DEADLOCK*. --- The following scenario would explain why CASE 2 is problematic. THREAD X THREAD Y lock L with depth n lock L' with depth n lock A lock A lock_nested L' with depth n + 1 lock_nested L'' with depth n + 1 ... ... unlock L' unlock L'' unlock A unlock A unlock L unlock L' Yes. I need to check if the report you shared with me is a true one, but it's not because DEPT doesn't work with *_nested() APIs. Byungchul
