Explain why we need to disable softirqs while processing callbacks in
an offline fashion. The subtle reason doesn't want to be forgotten.
Reported-by: Boqun Feng <boqun.f...@gmail.com>
Reported-by: Paul E. McKenney <paul...@kernel.org>
Cc: Josh Triplett <j...@joshtriplett.org>
Cc: Lai Jiangshan <jiangshan...@gmail.com>
Cc: Joel Fernandes <j...@joelfernandes.org>
Cc: Neeraj Upadhyay <neer...@codeaurora.org>
Cc: Boqun Feng <boqun.f...@gmail.com>
Signed-off-by: Frederic Weisbecker <frede...@kernel.org>
---
kernel/rcu/tree_plugin.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a44f80d7661b..dcfae03eb9e9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2235,6 +2235,12 @@ static void nocb_cb_wait(struct rcu_data *rdp)
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
+ /*
+ * While transitioning to/from NOCB mode, a CPU might execute the same
+ * callback concurrently if it requeues itself and the softirq
interrupts
+ * the offloaded callback processing. Make sure we disable BH to prevent
+ * from that.
+ */
local_bh_disable();
rcu_do_batch(rdp);
local_bh_enable();
--
2.25.1
