srcu: Check for readers at module-exit time
If a given statically allocated in-module srcu_struct structure was ever
used for updates, srcu_module_going() will invoke cleanup_srcu_struct()
at module-exit time. This will check for the error case of SRCU readers
persisting past module-exit time. On the other hand, if this srcu_struct
structure never went through a grace period, srcu_module_going() only
invokes free_percpu(), which would result in strange failures if SRCU
readers persisted past module-exit time.
This commit therefore adds a srcu_readers_active() check to
srcu_module_going(), splatting if readers have persisted and refraining
from invoking free_percpu() in that case. Better to leak memory than
to suffer silent memory corruption!
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 2495cbf..2b73cb1 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1915,7 +1915,8 @@ static void srcu_module_going(struct module *mod)
if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed)) &&
!WARN_ON_ONCE(!ssp->srcu_sup->sda_is_static))
cleanup_srcu_struct(ssp);
- free_percpu(ssp->sda);
+ else if (!WARN_ON(srcu_readers_active(ssp)))
+ free_percpu(ssp->sda);
}
}
