On Fri, 2017-03-24 at 13:20 -0700, Paul E. McKenney wrote: > > And I cannot resist adding this one: > > CPU 1 CPU 2 > i = srcu_read_lock(&s1); mutex_lock(&l1); > mutex_lock(&l1); synchronize_srcu(&s2); > mutex_unlock(&l1); mutex_unlock(&l1); > srcu_read_unlock(&s1, i); > > CPU 3 CPU 4 > i = srcu_read_lock(&s2); mutex_lock(&l2); > mutex_lock(&l2); synchronize_srcu(&s1); > mutex_unlock(&l2); mutex_unlock(&l2); > srcu_read_unlock(&s2, i); > > Removing the SRCU statements from any of these CPU would break the > deadlock. This can be easily extended to a deadlock cycle involving > any number of srcu_struct structures. > > But this would still be a cycle involving an srcu_read_lock() and a > synchronize_srcu() on the same srcu_struct, which is reassuring. Right, you can cycle this indefinitely. lockdep has some kind of maximum chain length I think. :) johannes
