Commit 7ea91307 authored by Zqiang's avatar Zqiang Committed by Joel Fernandes (Google)
Browse files

rcu: Permit start_poll_synchronize_rcu_expedited() to be invoked early 



According to the commit log of the patch that added it to the kernel,
start_poll_synchronize_rcu_expedited() can be invoked very early, as
in long before rcu_init() has been invoked.  But before rcu_init(),
the rcu_data structure's ->mynode field has not yet been initialized.
This means that the start_poll_synchronize_rcu_expedited() function's
attempt to set the CPU's leaf rcu_node structure's ->exp_seq_poll_rq
field will result in a segmentation fault.

This commit therefore causes start_poll_synchronize_rcu_expedited() to
set ->exp_seq_poll_rq only after rcu_init() has initialized all CPUs'
rcu_data structures' ->mynode fields.  It also removes the check from
the rcu_init() function so that start_poll_synchronize_rcu_expedited(
is unconditionally invoked.  Yes, this might result in an unnecessary
boot-time grace period, but this is down in the noise.

Signed-off-by: default avatarZqiang <qiang1.zhang@intel.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
parent 46103fe0

kernel/rcu/tree.c

+2 −3
Original line number Diff line number Diff line
@@ -4942,8 +4942,7 @@ void __init rcu_init(void) 
	else

		qovld_calc = qovld;



	// Kick-start any polled grace periods that started early.

	if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))

	// Kick-start in case any polled grace periods started early.

	(void)start_poll_synchronize_rcu_expedited();



	rcu_test_sync_prims();

kernel/rcu/tree_exp.h

+3 −2
Original line number Diff line number Diff line
@@ -1066,10 +1066,11 @@ unsigned long start_poll_synchronize_rcu_expedited(void) 
	if (rcu_init_invoked())

		raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);

	if (!poll_state_synchronize_rcu(s)) {

		if (rcu_init_invoked()) {

			rnp->exp_seq_poll_rq = s;

		if (rcu_init_invoked())

			queue_work(rcu_gp_wq, &rnp->exp_poll_wq);

		}

	}

	if (rcu_init_invoked())

		raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);