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rcu: Add READ_ONCE() to rcu_data ->gpwrap

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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: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-07 15:48:39 -08:00
parent 65bb0dc437
commit a5b8950180
2 changed files with 2 additions and 2 deletions
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2
kernel/rcu/tree.c
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@ -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;

2
kernel/rcu/tree_stall.h
View file

@ -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;