Commit 0937d045 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add READ_ONCE() to rcu_node ->gp_seq 



The rcu_node structure's ->gp_seq field is read locklessly, so this
commit adds the READ_ONCE() to several loads in order to avoid
destructive compiler optimizations.

This data race was reported by KCSAN.  Not appropriate for backporting
because this affects only tracing and warnings.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent b0c18c87

kernel/rcu/tree.c

+5 −4
Original line number Diff line number Diff line
@@ -1126,8 +1126,9 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,

			      unsigned long gp_seq_req, const char *s)

{

	trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req,

				      rnp->level, rnp->grplo, rnp->grphi, s);

	trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),

				      gp_seq_req, rnp->level,

				      rnp->grplo, rnp->grphi, s);

}



/*
@@ -1904,7 +1905,7 @@ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, 
		rnp_c = rnp;

		rnp = rnp->parent;

		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		oldmask = rnp_c->qsmask;

		oldmask = READ_ONCE(rnp_c->qsmask);

	}



	/*
@@ -2052,7 +2053,7 @@ int rcutree_dying_cpu(unsigned int cpu) 
		return 0;



	blkd = !!(rnp->qsmask & rdp->grpmask);

	trace_rcu_grace_period(rcu_state.name, rnp->gp_seq,

	trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),

			       blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));

	return 0;

}

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