On Thu, Apr 21, 2022 at 12:22:11PM +0800, Hillf Danton wrote: > Given rcu_lock_acquire() in srcu_read_lock(), > > iA = srcu_read_lock(foo); > iB = srcu_read_lock(foo); // not bar > ... > srcu_read_unlock(foo, iB); > srcu_read_unlock(foo, iA); > > can the call sequence above trigger warning with CONFIG_DEBUG_LOCK_ALLOC enabled? I hope not! After all, nesting SRCU read-side critical sections is perfectly legal. But why not just try it and see? > Does it make sense to add srcu_lock_acquire() in line with rwsem_acquire_read() if > warning is expected but not triggered? Please understand that while SRCU can often be used where an rwsem might otherwise be used, SRCU is not an rwsem. For one thing, rwsem readers can deadlock in ways that SRCU reader cannot. Now, I don't yet know of a non-destructive use case for partially overlapping SRCU read-side critical sections, for example, if you switched the two srcu_read_unlock() calls above. But at the same time, I cannot prove that there is no valid use case, not yet, anyway. Thanx, Paul > Thanks > Hillf > > static inline void rcu_lock_acquire(struct lockdep_map *map) > { > lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); > } > > static inline void srcu_lock_acquire(struct lockdep_map *map) > { > lock_acquire(map, 0, 0, 1, 0, NULL, _THIS_IP_); > }