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rcu: Add WRITE_ONCE() to rcu_node ->qsmaskinitnext

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The rcu_state structure's ->qsmaskinitnext field is read locklessly,
so this commit adds the WRITE_ONCE() to an update in order to provide
proper documentation and READ_ONCE()/WRITE_ONCE() pairing.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely for systems not doing incessant CPU-hotplug
operations.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-03 15:44:23 -08:00
parent 2906d2154c
commit 105abf82b0
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/tree.c
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@ -3379,7 +3379,7 @@ void rcu_cpu_starting(unsigned int cpu)
rnp = rdp->mynode;
mask = rdp->grpmask;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->qsmaskinitnext |= mask;
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
oldmask = rnp->expmaskinitnext;
rnp->expmaskinitnext |= mask;
oldmask ^= rnp->expmaskinitnext;
@ -3432,7 +3432,7 @@ void rcu_report_dead(unsigned int cpu)
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
}
rnp->qsmaskinitnext &= ~mask;
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
raw_spin_unlock(&rcu_state.ofl_lock);