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rcu: Add READ_ONCE and data_race() to rcu_node ->boost_tasks

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The rcu_node structure's ->boost_tasks field is read locklessly, so this
commit adds the READ_ONCE() to one load in order to avoid destructive
compiler optimizations.  The other load is from a diagnostic print,
so data_race() suffices.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-03 15:22:01 -08:00
parent 314eeb43e5
commit 065a6db12a
1 changed files with 3 additions and 2 deletions
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5
kernel/rcu/tree_plugin.h
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@ -760,7 +760,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n", pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext); __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n", pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
__func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks, __func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
READ_ONCE(rnp->exp_tasks)); READ_ONCE(rnp->exp_tasks));
pr_info("%s: ->blkd_tasks", __func__); pr_info("%s: ->blkd_tasks", __func__);
i = 0; i = 0;
@ -1036,7 +1036,8 @@ static int rcu_boost_kthread(void *arg)
for (;;) { for (;;) {
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING); WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
rcu_wait(rnp->boost_tasks || READ_ONCE(rnp->exp_tasks)); rcu_wait(READ_ONCE(rnp->boost_tasks) ||
READ_ONCE(rnp->exp_tasks));
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING); WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
more2boost = rcu_boost(rnp); more2boost = rcu_boost(rnp);