Commit a5b89501 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add READ_ONCE() to rcu_data ->gpwrap 



The rcu_data structure's ->gpwrap field is read locklessly, and so
this commit adds the required READ_ONCE() to a pair of laods in order
to avoid destructive compiler optimizations.

This data race was reported by KCSAN.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 65bb0dc4

kernel/rcu/tree.c

+1 −1
Original line number Diff line number Diff line
@@ -1322,7 +1322,7 @@ static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp, 


	rcu_lockdep_assert_cblist_protected(rdp);

	c = rcu_seq_snap(&rcu_state.gp_seq);

	if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {

	if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {

		/* Old request still live, so mark recent callbacks. */

		(void)rcu_segcblist_accelerate(&rdp->cblist, c);

		return;

kernel/rcu/tree_stall.h

+1 −1
Original line number Diff line number Diff line
@@ -602,7 +602,7 @@ void show_rcu_gp_kthreads(void) 
			continue;

		for_each_leaf_node_possible_cpu(rnp, cpu) {

			rdp = per_cpu_ptr(&rcu_data, cpu);

			if (rdp->gpwrap ||

			if (READ_ONCE(rdp->gpwrap) ||

			    ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),

					 READ_ONCE(rdp->gp_seq_needed)))

				continue;

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