Commit 5de2e5bb authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney
Browse files

rcu/nocb: Comment the reason behind BH disablement on batch processing 



This commit explains why softirqs need to be disabled while invoking
callbacks, even when callback processing has been offloaded.  After
all, invoking callbacks concurrently is one thing, but concurrently
invoking the same callback is quite another.

Reported-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Reported-by: default avatarPaul 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: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 3820b513

kernel/rcu/tree_plugin.h

+6 −0
Original line number Diff line number Diff line
@@ -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);

	/*

	 * Disable BH to provide the expected environment.  Also, when

	 * transitioning to/from NOCB mode, a self-requeuing callback might

	 * be invoked from softirq.  A short grace period could cause both

	 * instances of this callback would execute concurrently.

	 */

	local_bh_disable();

	rcu_do_batch(rdp);

	local_bh_enable();