The only thing that prevented an rdp leader from being de-offloaded was the nocb_bypass_timer that used to lock the nocb_lock of the rdp leader.
If an rdp gets de-offloaded, it will subtely ignore rcu_nocb_lock() calls and do its job in the timer unsafely. Worse yet: if it gets re-offloaded in the middle of the timer, rcu_nocb_unlock() would try to unlock, leaving it imbalanced.
Now that the nocb_bypass_timer doesn't use the nocb_lock anymore, we can safely allow rdp leader to be de-offloaded.
Reported-by: Paul E. McKenney paulmck@kernel.org Cc: Josh Triplett josh@joshtriplett.org Cc: Lai Jiangshan jiangshanlai@gmail.com Cc: Joel Fernandes joel@joelfernandes.org Cc: Neeraj Upadhyay neeraju@codeaurora.org Cc: Boqun Feng boqun.feng@gmail.com Signed-off-by: Frederic Weisbecker frederic@kernel.org --- kernel/rcu/tree_plugin.h | 4 ---- 1 file changed, 4 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 28ace1ae83d6..dae892ac570a 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2481,10 +2481,6 @@ int rcu_nocb_cpu_deoffload(int cpu) struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); int ret = 0;
- if (rdp == rdp->nocb_gp_rdp) { - pr_info("Can't deoffload an rdp GP leader (yet)\n"); - return -EINVAL; - } mutex_lock(&rcu_state.barrier_mutex); cpus_read_lock(); if (rcu_rdp_is_offloaded(rdp)) {