rcu: Add WRITE_ONCE() to rcu_node ->qsmaskinitnext (105abf82) · Commits · 戴 / test

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>

kernel/rcu/tree.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);

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