Commit 6f4cec22 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Paul E. McKenney
Browse files

rcu: Eliminate lockless accesses to rcu_sync->gp_count 



The rcu_sync structure's ->gp_count field is always accessed under the
protection of that same structure's ->rss_lock field, with the exception
of a pair of WARN_ON_ONCE() calls just prior to acquiring that lock in
functions rcu_sync_exit() and rcu_sync_dtor().  These lockless accesses
are unnecessary and impair KCSAN's ability to catch bugs that might be
inserted via other lockless accesses.

This commit therefore moves those WARN_ON_ONCE() calls under the lock.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 7f09e70f

kernel/rcu/sync.c

+4 −8
Original line number Diff line number Diff line
@@ -122,7 +122,7 @@ void rcu_sync_enter(struct rcu_sync *rsp) 
		 * we are called at early boot time but this shouldn't happen.

		 */

	}

	WRITE_ONCE(rsp->gp_count, rsp->gp_count + 1);

	rsp->gp_count++;

	spin_unlock_irq(&rsp->rss_lock);



	if (gp_state == GP_IDLE) {
@@ -151,15 +151,11 @@ void rcu_sync_enter(struct rcu_sync *rsp) 
 */

void rcu_sync_exit(struct rcu_sync *rsp)

{

	int gpc;



	WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_IDLE);

	WARN_ON_ONCE(READ_ONCE(rsp->gp_count) == 0);



	spin_lock_irq(&rsp->rss_lock);

	gpc = rsp->gp_count - 1;

	WRITE_ONCE(rsp->gp_count, gpc);

	if (!gpc) {

	WARN_ON_ONCE(rsp->gp_count == 0);

	if (!--rsp->gp_count) {

		if (rsp->gp_state == GP_PASSED) {

			WRITE_ONCE(rsp->gp_state, GP_EXIT);

			rcu_sync_call(rsp);
@@ -178,10 +174,10 @@ void rcu_sync_dtor(struct rcu_sync *rsp) 
{

	int gp_state;



	WARN_ON_ONCE(READ_ONCE(rsp->gp_count));

	WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_PASSED);



	spin_lock_irq(&rsp->rss_lock);

	WARN_ON_ONCE(rsp->gp_count);

	if (rsp->gp_state == GP_REPLAY)

		WRITE_ONCE(rsp->gp_state, GP_EXIT);

	gp_state = rsp->gp_state;