On Mon, Feb 13, 2023 at 05:51:11PM -0800, Boqun Feng wrote: > Basically if you have two lock instances A and B with the same class, > and you know that locking ordering is always A -> B, then you can do > > mutex_lock(A); > mutex_lock_nest_lock(B, A); // lock B. > > to tell the lockdep this is not deadlock, plus lockdep will treat the > acquisition of A and the precondition of acquisition B, so the following > is not a deadlock as well: > > T1: > mutex_lock(A); > mutex_lock(C); > mutex_lock_nest_lock(B, A); > > T2: > mutex_lock(A); > mutex_lock_nest_lock(B, A); > mutex_lock(C); Why isn't this treated as a deadlock? It sure looks like a deadlock to me. Is this an example where lockdep just doesn't get the right answer? Alan Stern
