From 552cac80e65f38a0cc9022456c09efed7e88f9d6 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 23 Feb 2021 01:10:06 +0100 Subject: [PATCH] rcu/nocb: Allow de-offloading rdp leader 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 subtlely 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, de-offloading the rdp leader is now safe. This commit therefore allows the rdp leader to be de-offloaded. Reported-by: Paul E. McKenney Cc: Josh Triplett Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Boqun Feng Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- 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 82e9ffb92347..015adec5bdc5 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2489,10 +2489,6 @@ 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)) {